diff --git a/schemars/src/json_schema_impls/core.rs b/schemars/src/json_schema_impls/core.rs
index 5cefbdd..647030f 100644
--- a/schemars/src/json_schema_impls/core.rs
+++ b/schemars/src/json_schema_impls/core.rs
@@ -62,13 +62,17 @@ impl<T: JsonSchema> JsonSchema for Option<T> {
         parent: &mut SchemaObject,
         name: String,
         metadata: Option<Metadata>,
-        _required: bool,
+        required: Option<bool>,
     ) {
-        let mut schema = gen.subschema_for::<Self>();
-        schema = gen.apply_metadata(schema, metadata);
+        if required == Some(true) {
+            T::add_schema_as_property(gen, parent, name, metadata, required)
+        } else {
+            let mut schema = gen.subschema_for::<Self>();
+            schema = gen.apply_metadata(schema, metadata);
 
-        let object = parent.object();
-        object.properties.insert(name, schema);
+            let object = parent.object();
+            object.properties.insert(name, schema);
+        }
     }
 }
 
diff --git a/schemars/src/json_schema_impls/mod.rs b/schemars/src/json_schema_impls/mod.rs
index d493ea0..4d96ee2 100644
--- a/schemars/src/json_schema_impls/mod.rs
+++ b/schemars/src/json_schema_impls/mod.rs
@@ -30,7 +30,7 @@ macro_rules! forward_impl {
                 parent: &mut crate::schema::SchemaObject,
                 name: String,
                 metadata: Option<crate::schema::Metadata>,
-                required: bool,
+                required: Option<bool>,
             ) {
                 <$target>::add_schema_as_property(gen, parent, name, metadata, required)
             }
diff --git a/schemars/src/lib.rs b/schemars/src/lib.rs
index eb6d5ac..9a9e65c 100644
--- a/schemars/src/lib.rs
+++ b/schemars/src/lib.rs
@@ -375,13 +375,13 @@ pub trait JsonSchema {
         parent: &mut SchemaObject,
         name: String,
         metadata: Option<schema::Metadata>,
-        required: bool,
+        required: Option<bool>,
     ) {
         let mut schema = gen.subschema_for::<Self>();
         schema = gen.apply_metadata(schema, metadata);
 
         let object = parent.object();
-        if required {
+        if required.unwrap_or(true) {
             object.required.insert(name.clone());
         }
         object.properties.insert(name, schema);
diff --git a/schemars/src/schema.rs b/schemars/src/schema.rs
index a4c6e32..e9a0124 100644
--- a/schemars/src/schema.rs
+++ b/schemars/src/schema.rs
@@ -9,6 +9,7 @@ use crate::JsonSchema;
 use crate::{Map, Set};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
+use std::ops::Deref;
 
 /// A JSON Schema.
 #[allow(clippy::large_enum_variant)]
@@ -191,7 +192,13 @@ where
 macro_rules! get_or_insert_default_fn {
     ($name:ident, $ret:ty) => {
         get_or_insert_default_fn!(
-            concat!("Returns a mutable reference to this schema's [`", stringify!($ret), "`](#structfield.", stringify!($name), "), creating it if it was `None`."),
+            concat!(
+                "Returns a mutable reference to this schema's [`",
+                stringify!($ret),
+                "`](#structfield.",
+                stringify!($name),
+                "), creating it if it was `None`."
+            ),
             $name,
             $ret
         );
@@ -224,6 +231,13 @@ impl SchemaObject {
         self.reference.is_some()
     }
 
+    // TODO document
+    pub fn has_type(&self, ty: InstanceType) -> bool {
+        self.instance_type
+            .as_ref()
+            .map_or(true, |x| x.contains(&ty))
+    }
+
     get_or_insert_default_fn!(metadata, Metadata);
     get_or_insert_default_fn!(subschemas, SubschemaValidation);
     get_or_insert_default_fn!(number, NumberValidation);
@@ -506,3 +520,13 @@ impl<T> From<Vec<T>> for SingleOrVec<T> {
         SingleOrVec::Vec(vec)
     }
 }
+
+impl<T: PartialEq> SingleOrVec<T> {
+    // TODO document
+    pub fn contains(&self, x: &T) -> bool {
+        match self {
+            SingleOrVec::Single(s) => s.deref() == x,
+            SingleOrVec::Vec(v) => v.contains(x),
+        }
+    }
+}
diff --git a/schemars/tests/expected/validate.json b/schemars/tests/expected/validate.json
new file mode 100644
index 0000000..228f249
--- /dev/null
+++ b/schemars/tests/expected/validate.json
@@ -0,0 +1,81 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Struct",
+  "type": "object",
+  "required": [
+    "contains_str1",
+    "contains_str2",
+    "email_address",
+    "homepage",
+    "map_contains",
+    "min_max",
+    "non_empty_str",
+    "pair",
+    "regex_str1",
+    "regex_str2",
+    "required_option",
+    "tel"
+  ],
+  "properties": {
+    "min_max": {
+      "type": "number",
+      "format": "float",
+      "maximum": 100.0,
+      "minimum": 0.01
+    },
+    "regex_str1": {
+      "type": "string",
+      "pattern": "^[Hh]ello\\b"
+    },
+    "regex_str2": {
+      "type": "string",
+      "pattern": "^[Hh]ello\\b"
+    },
+    "contains_str1": {
+      "type": "string",
+      "pattern": "substring\\.\\.\\."
+    },
+    "contains_str2": {
+      "type": "string",
+      "pattern": "substring\\.\\.\\."
+    },
+    "email_address": {
+      "type": "string",
+      "format": "email"
+    },
+    "tel": {
+      "type": "string",
+      "format": "phone"
+    },
+    "homepage": {
+      "type": "string",
+      "format": "uri"
+    },
+    "non_empty_str": {
+      "type": "string",
+      "maxLength": 100,
+      "minLength": 1
+    },
+    "pair": {
+      "type": "array",
+      "items": {
+        "type": "integer",
+        "format": "int32"
+      },
+      "maxItems": 2,
+      "minItems": 2
+    },
+    "map_contains": {
+      "type": "object",
+      "required": [
+        "map_key"
+      ],
+      "additionalProperties": {
+        "type": "null"
+      }
+    },
+    "required_option": {
+      "type": "boolean"
+    }
+  }
+}
\ No newline at end of file
diff --git a/schemars/tests/validate.rs b/schemars/tests/validate.rs
new file mode 100644
index 0000000..6d67531
--- /dev/null
+++ b/schemars/tests/validate.rs
@@ -0,0 +1,40 @@
+mod util;
+use schemars::JsonSchema;
+use std::collections::HashMap;
+use util::*;
+
+// In real code, this would typically be a Regex, potentially created in a `lazy_static!`.
+static STARTS_WITH_HELLO: &'static str = r"^[Hh]ello\b";
+
+#[derive(Debug, JsonSchema)]
+pub struct Struct {
+    #[validate(range(min = 0.01, max = 100))]
+    min_max: f32,
+    #[validate(regex = "STARTS_WITH_HELLO")]
+    regex_str1: String,
+    #[validate(regex(path = "STARTS_WITH_HELLO", code = "foo"))]
+    regex_str2: String,
+    #[validate(contains = "substring...")]
+    contains_str1: String,
+    #[validate(contains(pattern = "substring...", message = "bar"))]
+    contains_str2: String,
+    #[validate(email)]
+    email_address: String,
+    #[validate(phone)]
+    tel: String,
+    #[validate(url)]
+    homepage: String,
+    #[validate(length(min = 1, max = 100))]
+    non_empty_str: String,
+    #[validate(length(equal = 2))]
+    pair: Vec<i32>,
+    #[validate(contains = "map_key")]
+    map_contains: HashMap<String, ()>,
+    #[validate(required)]
+    required_option: Option<bool>,
+}
+
+#[test]
+fn validate() -> TestResult {
+    test_default_generated_schema::<Struct>("validate")
+}
diff --git a/schemars_derive/src/ast/from_serde.rs b/schemars_derive/src/ast/from_serde.rs
index 0d9add3..db2e092 100644
--- a/schemars_derive/src/ast/from_serde.rs
+++ b/schemars_derive/src/ast/from_serde.rs
@@ -73,6 +73,7 @@ impl<'a> FromSerde for Field<'a> {
             ty: serde.ty,
             original: serde.original,
             attrs: Attrs::new(&serde.original.attrs, errors),
+            validation_attrs: ValidationAttrs::new(&serde.original.attrs),
         })
     }
 }
diff --git a/schemars_derive/src/ast/mod.rs b/schemars_derive/src/ast/mod.rs
index a394acd..99fe188 100644
--- a/schemars_derive/src/ast/mod.rs
+++ b/schemars_derive/src/ast/mod.rs
@@ -1,6 +1,6 @@
 mod from_serde;
 
-use crate::attr::Attrs;
+use crate::attr::{Attrs, ValidationAttrs};
 use from_serde::FromSerde;
 use serde_derive_internals::ast as serde_ast;
 use serde_derive_internals::{Ctxt, Derive};
@@ -34,6 +34,7 @@ pub struct Field<'a> {
     pub ty: &'a syn::Type,
     pub original: &'a syn::Field,
     pub attrs: Attrs,
+    pub validation_attrs: ValidationAttrs,
 }
 
 impl<'a> Container<'a> {
diff --git a/schemars_derive/src/attr/mod.rs b/schemars_derive/src/attr/mod.rs
index 65667d9..d7a6628 100644
--- a/schemars_derive/src/attr/mod.rs
+++ b/schemars_derive/src/attr/mod.rs
@@ -1,7 +1,9 @@
 mod doc;
 mod schemars_to_serde;
+mod validation;
 
 pub use schemars_to_serde::process_serde_attrs;
+pub use validation::ValidationAttrs;
 
 use proc_macro2::{Group, Span, TokenStream, TokenTree};
 use quote::ToTokens;
diff --git a/schemars_derive/src/attr/validation.rs b/schemars_derive/src/attr/validation.rs
new file mode 100644
index 0000000..8f13168
--- /dev/null
+++ b/schemars_derive/src/attr/validation.rs
@@ -0,0 +1,308 @@
+use super::parse_lit_str;
+use proc_macro2::TokenStream;
+use syn::ExprLit;
+use syn::NestedMeta;
+use syn::{Expr, Lit, Meta, MetaNameValue, Path};
+
+#[derive(Debug, Default)]
+pub struct ValidationAttrs {
+    pub length_min: Option<Expr>,
+    pub length_max: Option<Expr>,
+    pub length_equal: Option<Expr>,
+    pub range_min: Option<Expr>,
+    pub range_max: Option<Expr>,
+    pub regex: Option<Path>,
+    pub contains: Option<String>,
+    pub required: bool,
+    pub format: Option<&'static str>,
+}
+
+impl ValidationAttrs {
+    pub fn new(attrs: &[syn::Attribute]) -> Self {
+        // TODO allow setting "validate" attributes through #[schemars(...)]
+        ValidationAttrs::default().populate(attrs)
+    }
+
+    fn populate(mut self, attrs: &[syn::Attribute]) -> Self {
+        // TODO don't silently ignore unparseable attributes
+        for meta_item in attrs
+            .iter()
+            .flat_map(|attr| get_meta_items(attr, "validate"))
+            .flatten()
+        {
+            match &meta_item {
+                NestedMeta::Meta(Meta::List(meta_list)) if meta_list.path.is_ident("length") => {
+                    for nested in meta_list.nested.iter() {
+                        match nested {
+                            NestedMeta::Meta(Meta::NameValue(nv)) if nv.path.is_ident("min") => {
+                                self.length_min = str_or_num_to_expr(&nv.lit);
+                            }
+                            NestedMeta::Meta(Meta::NameValue(nv)) if nv.path.is_ident("max") => {
+                                self.length_max = str_or_num_to_expr(&nv.lit);
+                            }
+                            NestedMeta::Meta(Meta::NameValue(nv)) if nv.path.is_ident("equal") => {
+                                self.length_equal = str_or_num_to_expr(&nv.lit);
+                            }
+                            _ => {}
+                        }
+                    }
+                }
+
+                NestedMeta::Meta(Meta::List(meta_list)) if meta_list.path.is_ident("range") => {
+                    for nested in meta_list.nested.iter() {
+                        match nested {
+                            NestedMeta::Meta(Meta::NameValue(nv)) if nv.path.is_ident("min") => {
+                                self.range_min = str_or_num_to_expr(&nv.lit);
+                            }
+                            NestedMeta::Meta(Meta::NameValue(nv)) if nv.path.is_ident("max") => {
+                                self.range_max = str_or_num_to_expr(&nv.lit);
+                            }
+                            _ => {}
+                        }
+                    }
+                }
+
+                NestedMeta::Meta(m)
+                    if m.path().is_ident("required") || m.path().is_ident("required_nested") =>
+                {
+                    self.required = true;
+                }
+
+                NestedMeta::Meta(m) if m.path().is_ident("email") => {
+                    self.format = Some("email");
+                }
+
+                NestedMeta::Meta(m) if m.path().is_ident("url") => {
+                    self.format = Some("uri");
+                }
+
+                NestedMeta::Meta(m) if m.path().is_ident("phone") => {
+                    self.format = Some("phone");
+                }
+
+                NestedMeta::Meta(Meta::NameValue(MetaNameValue {
+                    path,
+                    lit: Lit::Str(regex),
+                    ..
+                })) if path.is_ident("regex") => self.regex = parse_lit_str(regex).ok(),
+
+                NestedMeta::Meta(Meta::List(meta_list)) if meta_list.path.is_ident("regex") => {
+                    self.regex = meta_list.nested.iter().find_map(|x| match x {
+                        NestedMeta::Meta(Meta::NameValue(MetaNameValue {
+                            path,
+                            lit: Lit::Str(regex),
+                            ..
+                        })) if path.is_ident("path") => parse_lit_str(regex).ok(),
+                        _ => None,
+                    });
+                }
+
+                NestedMeta::Meta(Meta::NameValue(MetaNameValue {
+                    path,
+                    lit: Lit::Str(contains),
+                    ..
+                })) if path.is_ident("contains") => self.contains = Some(contains.value()),
+
+                NestedMeta::Meta(Meta::List(meta_list)) if meta_list.path.is_ident("contains") => {
+                    self.contains = meta_list.nested.iter().find_map(|x| match x {
+                        NestedMeta::Meta(Meta::NameValue(MetaNameValue {
+                            path,
+                            lit: Lit::Str(contains),
+                            ..
+                        })) if path.is_ident("pattern") => Some(contains.value()),
+                        _ => None,
+                    });
+                }
+
+                _ => {}
+            }
+        }
+        self
+    }
+
+    pub fn validation_statements(&self, field_name: &str) -> TokenStream {
+        // Assume that the result will be interpolated in a context with the local variable
+        // `schema_object` - the SchemaObject for the struct that contains this field.
+        let mut statements = Vec::new();
+
+        if self.required {
+            statements.push(quote! {
+                schema_object.object().required.insert(#field_name.to_owned());
+            });
+        }
+
+        let mut array_validation = Vec::new();
+        let mut number_validation = Vec::new();
+        let mut object_validation = Vec::new();
+        let mut string_validation = Vec::new();
+
+        if let Some(length_min) = self
+            .length_min
+            .as_ref()
+            .or_else(|| self.length_equal.as_ref())
+        {
+            string_validation.push(quote! {
+                validation.min_length = Some(#length_min as u32);
+            });
+            array_validation.push(quote! {
+                validation.min_items = Some(#length_min as u32);
+            });
+        }
+
+        if let Some(length_max) = self
+            .length_max
+            .as_ref()
+            .or_else(|| self.length_equal.as_ref())
+        {
+            string_validation.push(quote! {
+                validation.max_length = Some(#length_max as u32);
+            });
+            array_validation.push(quote! {
+                validation.max_items = Some(#length_max as u32);
+            });
+        }
+
+        if let Some(range_min) = &self.range_min {
+            number_validation.push(quote! {
+                validation.minimum = Some(#range_min as f64);
+            });
+        }
+
+        if let Some(range_max) = &self.range_max {
+            number_validation.push(quote! {
+                validation.maximum = Some(#range_max as f64);
+            });
+        }
+
+        if let Some(regex) = &self.regex {
+            string_validation.push(quote! {
+                validation.pattern = Some(#regex.to_string());
+            });
+        }
+
+        if let Some(contains) = &self.contains {
+            object_validation.push(quote! {
+                validation.required.insert(#contains.to_string());
+            });
+
+            if self.regex.is_none() {
+                let pattern = crate::regex_syntax::escape(contains);
+                string_validation.push(quote! {
+                    validation.pattern = Some(#pattern.to_string());
+                });
+            }
+        }
+
+        let format = self.format.as_ref().map(|f| {
+            quote! {
+                prop_schema_object.format = Some(#f.to_string());
+            }
+        });
+
+        let array_validation = wrap_array_validation(array_validation);
+        let number_validation = wrap_number_validation(number_validation);
+        let object_validation = wrap_object_validation(object_validation);
+        let string_validation = wrap_string_validation(string_validation);
+
+        if array_validation.is_some()
+            || number_validation.is_some()
+            || object_validation.is_some()
+            || string_validation.is_some()
+            || format.is_some()
+        {
+            statements.push(quote! {
+                if let Some(schemars::schema::Schema::Object(prop_schema_object)) = schema_object
+                    .object
+                    .as_mut()
+                    .and_then(|o| o.properties.get_mut(#field_name))
+                {
+                    #array_validation
+                    #number_validation
+                    #object_validation
+                    #string_validation
+                    #format
+                }
+            });
+        }
+
+        statements.into_iter().collect()
+    }
+}
+
+fn wrap_array_validation(v: Vec<TokenStream>) -> Option<TokenStream> {
+    if v.is_empty() {
+        None
+    } else {
+        Some(quote! {
+            if prop_schema_object.has_type(schemars::schema::InstanceType::Array) {
+                let validation = prop_schema_object.array();
+                #(#v)*
+            }
+        })
+    }
+}
+
+fn wrap_number_validation(v: Vec<TokenStream>) -> Option<TokenStream> {
+    if v.is_empty() {
+        None
+    } else {
+        Some(quote! {
+            if prop_schema_object.has_type(schemars::schema::InstanceType::Integer)
+                || prop_schema_object.has_type(schemars::schema::InstanceType::Number) {
+                let validation = prop_schema_object.number();
+                #(#v)*
+            }
+        })
+    }
+}
+
+fn wrap_object_validation(v: Vec<TokenStream>) -> Option<TokenStream> {
+    if v.is_empty() {
+        None
+    } else {
+        Some(quote! {
+            if prop_schema_object.has_type(schemars::schema::InstanceType::Object) {
+                let validation = prop_schema_object.object();
+                #(#v)*
+            }
+        })
+    }
+}
+
+fn wrap_string_validation(v: Vec<TokenStream>) -> Option<TokenStream> {
+    if v.is_empty() {
+        None
+    } else {
+        Some(quote! {
+            if prop_schema_object.has_type(schemars::schema::InstanceType::String) {
+                let validation = prop_schema_object.string();
+                #(#v)*
+            }
+        })
+    }
+}
+
+fn get_meta_items(
+    attr: &syn::Attribute,
+    attr_type: &'static str,
+) -> Result<Vec<syn::NestedMeta>, ()> {
+    if !attr.path.is_ident(attr_type) {
+        return Ok(Vec::new());
+    }
+
+    match attr.parse_meta() {
+        Ok(Meta::List(meta)) => Ok(meta.nested.into_iter().collect()),
+        _ => Err(()),
+    }
+}
+
+fn str_or_num_to_expr(lit: &Lit) -> Option<Expr> {
+    match lit {
+        Lit::Str(s) => parse_lit_str::<syn::ExprPath>(s).ok().map(Expr::Path),
+        Lit::Int(_) | Lit::Float(_) => Some(Expr::Lit(ExprLit {
+            attrs: Vec::new(),
+            lit: lit.clone(),
+        })),
+        _ => None,
+    }
+}
diff --git a/schemars_derive/src/lib.rs b/schemars_derive/src/lib.rs
index c81eb40..c737380 100644
--- a/schemars_derive/src/lib.rs
+++ b/schemars_derive/src/lib.rs
@@ -9,12 +9,13 @@ extern crate proc_macro;
 mod ast;
 mod attr;
 mod metadata;
+mod regex_syntax;
 mod schema_exprs;
 
 use ast::*;
 use proc_macro2::TokenStream;
 
-#[proc_macro_derive(JsonSchema, attributes(schemars, serde))]
+#[proc_macro_derive(JsonSchema, attributes(schemars, serde, validate))]
 pub fn derive_json_schema_wrapper(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse_macro_input!(input as syn::DeriveInput);
     derive_json_schema(input, false)
@@ -72,7 +73,7 @@ fn derive_json_schema(
                         parent: &mut schemars::schema::SchemaObject,
                         name: String,
                         metadata: Option<schemars::schema::Metadata>,
-                        required: bool,
+                        required: Option<bool>,
                     ) {
                         <#ty as schemars::JsonSchema>::add_schema_as_property(gen, parent, name, metadata, required)
                     }
diff --git a/schemars_derive/src/regex_syntax.rs b/schemars_derive/src/regex_syntax.rs
new file mode 100644
index 0000000..353bf8d
--- /dev/null
+++ b/schemars_derive/src/regex_syntax.rs
@@ -0,0 +1,26 @@
+// Copied from regex_syntax crate to avoid pulling in the whole crate just for a utility function
+// https://github.com/rust-lang/regex/blob/ff283badce21dcebd581909d38b81f2c8c9bfb54/regex-syntax/src/lib.rs
+
+pub fn escape(text: &str) -> String {
+    let mut quoted = String::new();
+    escape_into(text, &mut quoted);
+    quoted
+}
+
+fn escape_into(text: &str, buf: &mut String) {
+    buf.reserve(text.len());
+    for c in text.chars() {
+        if is_meta_character(c) {
+            buf.push('\\');
+        }
+        buf.push(c);
+    }
+}
+
+fn is_meta_character(c: char) -> bool {
+    match c {
+        '\\' | '.' | '+' | '*' | '?' | '(' | ')' | '|' | '[' | ']' | '{' | '}' | '^' | '$'
+        | '#' | '&' | '-' | '~' => true,
+        _ => false,
+    }
+}
diff --git a/schemars_derive/src/schema_exprs.rs b/schemars_derive/src/schema_exprs.rs
index a5cf2ca..4965fd5 100644
--- a/schemars_derive/src/schema_exprs.rs
+++ b/schemars_derive/src/schema_exprs.rs
@@ -390,32 +390,43 @@ fn expr_for_struct(
 
     let mut type_defs = Vec::new();
 
-    let properties: Vec<_> = property_fields.into_iter().map(|field| {
-        let name = field.name();
-        let default = field_default_expr(field, set_container_default.is_some());
+    let properties: Vec<_> = property_fields
+        .into_iter()
+        .map(|field| {
+            let name = field.name();
+            let default = field_default_expr(field, set_container_default.is_some());
 
-        let required = match default {
-            Some(_) => quote!(false),
-            None => quote!(true),
-        };
+            let required = match (&default, field.validation_attrs.required) {
+                (Some(_), _) => quote!(Some(false)),
+                (None, false) => quote!(None),
+                (None, true) => quote!(Some(true)),
+            };
 
-        let metadata = &SchemaMetadata {
-            read_only: field.serde_attrs.skip_deserializing(),
-            write_only: field.serde_attrs.skip_serializing(),
-            default,
-            ..SchemaMetadata::from_attrs(&field.attrs)
-        };
+            let metadata = &SchemaMetadata {
+                read_only: field.serde_attrs.skip_deserializing(),
+                write_only: field.serde_attrs.skip_serializing(),
+                default,
+                ..SchemaMetadata::from_attrs(&field.attrs)
+            };
 
-        let (ty, type_def) = type_for_schema(field, type_defs.len());
-        if let Some(type_def) = type_def {
-            type_defs.push(type_def);
-        }
+            let (ty, type_def) = type_for_schema(field, type_defs.len());
+            if let Some(type_def) = type_def {
+                type_defs.push(type_def);
+            }
 
-        quote_spanned! {ty.span()=>
-            <#ty as schemars::JsonSchema>::add_schema_as_property(gen, &mut schema_object, #name.to_owned(), #metadata, #required);
-        }
+            let validation = field.validation_attrs.validation_statements(&name);
 
-    }).collect();
+            quote_spanned! {ty.span()=>
+                <#ty as schemars::JsonSchema>::add_schema_as_property(
+                    gen,
+                    &mut schema_object,
+                    #name.to_owned(),
+                    #metadata,
+                    #required);
+                #validation
+            }
+        })
+        .collect();
 
     let flattens: Vec<_> = flattened_fields
         .into_iter()