diff --git a/README.md b/README.md
index fe797e1..55dcc85 100644
--- a/README.md
+++ b/README.md
@@ -153,6 +153,8 @@ Fine provides implementations for the following types:
 | `std::vector<T>`                     | x       | x       | `list(a)`                   |
 | `std::map<K, V>`                     | x       | x       | `%{k => v}`                 |
 | `std::unordered_map<K, V>`           | x       | x       | `%{k => v}`                 |
+| `std::multimap<K, V>`                | x       | x       | `list({k, v})`              |
+| `std::unordered_multimap<K, V>`      | x       | x       | `list({k, v})`              |
 | `fine::ResourcePtr<T>`               | x       | x       | `reference`                 |
 | `T` with [struct metadata](#structs) | x       | x       | `%a{}`                      |
 | `fine::Ok<Args...>`                  | x       |         | `{:ok, ...}`                |
diff --git a/c_include/fine.hpp b/c_include/fine.hpp
index 7a31677..0041d3f 100644
--- a/c_include/fine.hpp
+++ b/c_include/fine.hpp
@@ -381,14 +381,14 @@ inline Term make_new_binary(ErlNifEnv *env, const char *data, size_t size) {
 //
 // The given type must have a specialized Decoder<T> implementation.
 template <typename T> T decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
-  return Decoder<T>::decode(env, term);
+  return Decoder<std::remove_cv_t<T>>::decode(env, term);
 }
 
 // Encodes the given value as a Erlang term.
 //
 // The value type must have a specialized Encoder<T> implementation.
 template <typename T> ERL_NIF_TERM encode(ErlNifEnv *env, const T &value) {
-  return Encoder<T>::encode(env, value);
+  return Encoder<std::remove_cv_t<T>>::encode(env, value);
 }
 
 // We want decode to return the value, and since the argument types
@@ -473,9 +473,10 @@ template <> struct Decoder<ErlNifPid> {
     }
     if (!enif_get_local_pid(env, term, &pid)) {
       // If the term is a PID and it is not local, it means it's a remote PID.
-      throw std::invalid_argument(
-          "decode failed, expected a local pid, but got a remote one. NIFs can "
-          "only send messages to local PIDs and remote PIDs cannot be decoded");
+      throw std::invalid_argument("decode failed, expected a local pid, but "
+                                  "got a remote one. NIFs can "
+                                  "only send messages to local PIDs and "
+                                  "remote PIDs cannot be decoded");
     }
     return pid;
   }
@@ -591,6 +592,25 @@ template <typename... Args> struct Decoder<std::tuple<Args...>> {
   }
 };
 
+template <typename T1, typename T2> struct Decoder<std::pair<T1, T2>> {
+  static std::pair<T1, T2> decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
+    int size;
+    const ERL_NIF_TERM *terms;
+    if (!enif_get_tuple(env, term, &size, &terms)) {
+      throw std::invalid_argument("decode failed, expected a tuple");
+    }
+
+    if (size != 2) {
+      throw std::invalid_argument(
+          "decode failed, expected tuple to have 2 elements, but had " +
+          std::to_string(size));
+    }
+
+    return std::make_pair(fine::decode<T1>(env, terms[0]),
+                          fine::decode<T2>(env, terms[1]));
+  }
+};
+
 template <typename T, typename Alloc> struct Decoder<std::vector<T, Alloc>> {
   static std::vector<T, Alloc> decode(ErlNifEnv *env,
                                       const ERL_NIF_TERM &term) {
@@ -690,6 +710,60 @@ struct Decoder<std::unordered_map<K, V, Hash, Pred, Alloc>> {
   };
 };
 
+template <typename K, typename V, typename Compare, typename Alloc>
+struct Decoder<std::multimap<K, V, Compare, Alloc>> {
+  static std::multimap<K, V, Compare, Alloc> decode(ErlNifEnv *env,
+                                                    const ERL_NIF_TERM &term) {
+    unsigned int length;
+
+    if (!enif_get_list_length(env, term, &length)) {
+      throw std::invalid_argument("decode failed, expected a list");
+    }
+
+    std::multimap<K, V, Compare, Alloc> map;
+
+    auto list = term;
+
+    ERL_NIF_TERM head, tail;
+    while (enif_get_list_cell(env, list, &head, &tail)) {
+      auto entry = fine::decode<std::pair<const K, V>>(env, head);
+
+      map.emplace(std::move(entry));
+
+      list = tail;
+    }
+
+    return map;
+  }
+};
+
+template <typename K, typename V, typename Hash, typename Pred, typename Alloc>
+struct Decoder<std::unordered_multimap<K, V, Hash, Pred, Alloc>> {
+  static std::unordered_multimap<K, V, Hash, Pred, Alloc>
+  decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
+    unsigned int length;
+
+    if (!enif_get_list_length(env, term, &length)) {
+      throw std::invalid_argument("decode failed, expected a list");
+    }
+
+    std::unordered_multimap<K, V, Hash, Pred, Alloc> map;
+
+    auto list = term;
+
+    ERL_NIF_TERM head, tail;
+    while (enif_get_list_cell(env, list, &head, &tail)) {
+      auto entry = fine::decode<std::pair<const K, V>>(env, head);
+
+      map.emplace(std::move(entry));
+
+      list = tail;
+    }
+
+    return map;
+  }
+};
+
 template <typename T> struct Decoder<ResourcePtr<T>> {
   static ResourcePtr<T> decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
     void *ptr;
@@ -892,6 +966,14 @@ template <typename... Args> struct Encoder<std::tuple<Args...>> {
   }
 };
 
+template <typename T1, typename T2> struct Encoder<std::pair<T1, T2>> {
+  static ERL_NIF_TERM encode(ErlNifEnv *env, const std::pair<T1, T2> &pair) {
+    const auto first = fine::encode<T1>(env, pair.first);
+    const auto second = fine::encode<T2>(env, pair.second);
+    return enif_make_tuple(env, 2, first, second);
+  }
+};
+
 template <typename T, typename Alloc> struct Encoder<std::vector<T, Alloc>> {
   static ERL_NIF_TERM encode(ErlNifEnv *env,
                              const std::vector<T, Alloc> &vector) {
@@ -956,6 +1038,39 @@ struct Encoder<std::unordered_map<K, V, Hash, Pred, Alloc>> {
   }
 };
 
+template <typename K, typename V, typename Compare, typename Alloc>
+struct Encoder<std::multimap<K, V, Compare, Alloc>> {
+  static ERL_NIF_TERM encode(ErlNifEnv *env,
+                             const std::multimap<K, V, Compare, Alloc> &map) {
+    auto terms = std::vector<ERL_NIF_TERM>();
+    terms.reserve(map.size());
+
+    for (const auto &entry : map) {
+      terms.emplace_back(fine::encode(env, entry));
+    }
+
+    return enif_make_list_from_array(env, terms.data(),
+                                     static_cast<unsigned int>(terms.size()));
+  }
+};
+
+template <typename K, typename V, typename Hash, typename Pred, typename Alloc>
+struct Encoder<std::unordered_multimap<K, V, Hash, Pred, Alloc>> {
+  static ERL_NIF_TERM
+  encode(ErlNifEnv *env,
+         const std::unordered_multimap<K, V, Hash, Pred, Alloc> &map) {
+    auto terms = std::vector<ERL_NIF_TERM>();
+    terms.reserve(map.size());
+
+    for (const auto &entry : map) {
+      terms.emplace_back(fine::encode(env, entry));
+    }
+
+    return enif_make_list_from_array(env, terms.data(),
+                                     static_cast<unsigned int>(terms.size()));
+  }
+};
+
 template <typename T> struct Encoder<ResourcePtr<T>> {
   static ERL_NIF_TERM encode(ErlNifEnv *env, const ResourcePtr<T> &resource) {
     return enif_make_resource(env, reinterpret_cast<void *>(resource.get()));
diff --git a/test/c_src/finest.cpp b/test/c_src/finest.cpp
index 8f1f6d6..c04ef4f 100644
--- a/test/c_src/finest.cpp
+++ b/test/c_src/finest.cpp
@@ -205,6 +205,7 @@ codec_map_atom_int64(ErlNifEnv *, std::map<fine::Atom, int64_t> term) {
   return term;
 }
 FINE_NIF(codec_map_atom_int64, 0);
+
 std::map<fine::Atom, int64_t, std::less<fine::Atom>,
          std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
 codec_map_atom_int64_alloc(
@@ -237,6 +238,46 @@ codec_unordered_map_atom_int64_alloc(
 }
 FINE_NIF(codec_unordered_map_atom_int64_alloc, 0);
 
+std::multimap<fine::Atom, int64_t>
+codec_multimap_atom_int64(ErlNifEnv *,
+                          std::multimap<fine::Atom, int64_t> term) {
+  return term;
+}
+FINE_NIF(codec_multimap_atom_int64, 0);
+
+std::multimap<
+    fine::Atom, int64_t, std::less<fine::Atom>,
+    std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+codec_multimap_atom_int64_alloc(
+    ErlNifEnv *,
+    std::multimap<
+        fine::Atom, int64_t, std::less<fine::Atom>,
+        std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+        term) {
+  return term;
+}
+FINE_NIF(codec_multimap_atom_int64_alloc, 0);
+
+std::unordered_multimap<fine::Atom, int64_t>
+codec_unordered_multimap_atom_int64(
+    ErlNifEnv *, std::unordered_multimap<fine::Atom, int64_t> term) {
+  return term;
+}
+FINE_NIF(codec_unordered_multimap_atom_int64, 0);
+
+std::unordered_multimap<
+    fine::Atom, int64_t, std::hash<fine::Atom>, std::equal_to<fine::Atom>,
+    std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+codec_unordered_multimap_atom_int64_alloc(
+    ErlNifEnv *,
+    std::unordered_multimap<
+        fine::Atom, int64_t, std::hash<fine::Atom>, std::equal_to<fine::Atom>,
+        std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+        term) {
+  return term;
+}
+FINE_NIF(codec_unordered_multimap_atom_int64_alloc, 0);
+
 fine::ResourcePtr<TestResource>
 codec_resource(ErlNifEnv *, fine::ResourcePtr<TestResource> term) {
   return term;
diff --git a/test/lib/finest/nif.ex b/test/lib/finest/nif.ex
index 0e97d5d..6f3426a 100644
--- a/test/lib/finest/nif.ex
+++ b/test/lib/finest/nif.ex
@@ -40,6 +40,10 @@ defmodule Finest.NIF do
   def codec_map_atom_int64_alloc(_term), do: err!()
   def codec_unordered_map_atom_int64(_term), do: err!()
   def codec_unordered_map_atom_int64_alloc(_term), do: err!()
+  def codec_multimap_atom_int64(_term), do: err!()
+  def codec_multimap_atom_int64_alloc(_term), do: err!()
+  def codec_unordered_multimap_atom_int64(_term), do: err!()
+  def codec_unordered_multimap_atom_int64_alloc(_term), do: err!()
   def codec_resource(_term), do: err!()
   def codec_struct(_term), do: err!()
   def codec_struct_exception(_term), do: err!()
diff --git a/test/test/finest_test.exs b/test/test/finest_test.exs
index 37a1a90..6570c78 100644
--- a/test/test/finest_test.exs
+++ b/test/test/finest_test.exs
@@ -233,6 +233,78 @@ defmodule FinestTest do
       end
     end
 
+    test "keyword" do
+      empty_keyword = []
+
+      small_keyword = [hello: 1, world: 2]
+
+      large_keyword =
+        0..64 |> Enum.map(fn x -> {:"a#{x}", x} end) |> Enum.to_list()
+
+      for keyword <- [empty_keyword, small_keyword, large_keyword] do
+        assert Enum.sort(NIF.codec_multimap_atom_int64(keyword)) == Enum.sort(keyword)
+        assert Enum.sort(NIF.codec_multimap_atom_int64_alloc(keyword)) == Enum.sort(keyword)
+        assert Enum.sort(NIF.codec_unordered_multimap_atom_int64(keyword)) == Enum.sort(keyword)
+
+        assert Enum.sort(NIF.codec_unordered_multimap_atom_int64_alloc(keyword)) ==
+                 Enum.sort(keyword)
+      end
+
+      invalid_keyword = 10
+
+      assert_raise ArgumentError, "decode failed, expected a list", fn ->
+        NIF.codec_multimap_atom_int64(invalid_keyword)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected a list", fn ->
+        NIF.codec_multimap_atom_int64_alloc(invalid_keyword)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected a list", fn ->
+        NIF.codec_unordered_multimap_atom_int64(invalid_keyword)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected a list", fn ->
+        NIF.codec_unordered_multimap_atom_int64_alloc(invalid_keyword)
+      end
+
+      keyword_with_invalid_key = [{"hello", 42}]
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_multimap_atom_int64(keyword_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_multimap_atom_int64_alloc(keyword_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_unordered_multimap_atom_int64(keyword_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_unordered_multimap_atom_int64_alloc(keyword_with_invalid_key)
+      end
+
+      keyword_with_invalid_value = [hello: 1.0]
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_multimap_atom_int64(keyword_with_invalid_value)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_multimap_atom_int64_alloc(keyword_with_invalid_value)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_unordered_multimap_atom_int64(keyword_with_invalid_value)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_unordered_multimap_atom_int64_alloc(keyword_with_invalid_value)
+      end
+    end
+
     test "resource" do
       resource = NIF.resource_create(self())
       assert is_reference(resource)