diff --git a/Sources/DataStructures/AVLTree.swift b/Sources/DataStructures/AVLTree.swift
index 6ea961e..546ec64 100644
--- a/Sources/DataStructures/AVLTree.swift
+++ b/Sources/DataStructures/AVLTree.swift
@@ -222,5 +222,8 @@ extension AVLTree.Node: Hashable where Key: Hashable, Value: Hashable {
     }
 }
 
+extension AVLTree.Node: Codable where Key: Codable, Value: Codable { }
+
 extension AVLTree: Equatable where Value: Equatable { }
 extension AVLTree: Hashable where Key: Hashable, Value: Hashable { }
+extension AVLTree: Codable where Key: Codable, Value: Codable { }
diff --git a/Sources/DataStructures/AdjacencyList.swift b/Sources/DataStructures/AdjacencyList.swift
index 0c8aff9..ce7d1ab 100644
--- a/Sources/DataStructures/AdjacencyList.swift
+++ b/Sources/DataStructures/AdjacencyList.swift
@@ -166,3 +166,4 @@ extension AdjacencyList {
 
 extension AdjacencyList: Equatable { }
 extension AdjacencyList: Hashable { }
+extension AdjacencyList: Codable where Node: Codable { }
diff --git a/Sources/DataStructures/Bimap.swift b/Sources/DataStructures/Bimap.swift
index 035d1ef..9c08aac 100644
--- a/Sources/DataStructures/Bimap.swift
+++ b/Sources/DataStructures/Bimap.swift
@@ -238,3 +238,4 @@ extension Bimap {
 
 extension Bimap: Equatable { }
 extension Bimap: Hashable { }
+extension Bimap: Codable where Key: Codable, Value: Codable { }
diff --git a/Sources/DataStructures/BinaryHeap.swift b/Sources/DataStructures/BinaryHeap.swift
index dbb0e9a..32a443c 100644
--- a/Sources/DataStructures/BinaryHeap.swift
+++ b/Sources/DataStructures/BinaryHeap.swift
@@ -129,3 +129,4 @@ public struct BinaryHeap <Element: Hashable, Value: Comparable> {
 
 extension BinaryHeap: Equatable { }
 extension BinaryHeap: Hashable where Value: Hashable { }
+extension BinaryHeap: Codable where Element: Codable, Value: Codable { }
diff --git a/Sources/DataStructures/BinarySearchTree.swift b/Sources/DataStructures/BinarySearchTree.swift
index 819355a..84a5064 100644
--- a/Sources/DataStructures/BinarySearchTree.swift
+++ b/Sources/DataStructures/BinarySearchTree.swift
@@ -155,3 +155,5 @@ extension BinarySearchTree: ExpressibleByArrayLiteral {
 
 extension BinarySearchTree: Equatable { }
 extension BinarySearchTree: Hashable where Value: Hashable { }
+
+// TODO: `Codable`
diff --git a/Sources/DataStructures/CircularArray.swift b/Sources/DataStructures/CircularArray.swift
index e69528d..f017798 100644
--- a/Sources/DataStructures/CircularArray.swift
+++ b/Sources/DataStructures/CircularArray.swift
@@ -193,3 +193,4 @@ extension Array {
 
 extension CircularArray: Equatable where Element: Equatable { }
 extension CircularArray: Hashable where Element: Hashable { }
+extension CircularArray: Codable where Element: Codable { }
diff --git a/Sources/DataStructures/ContiguousSegmentCollection/ContiguousSegmentCollection.swift b/Sources/DataStructures/ContiguousSegmentCollection/ContiguousSegmentCollection.swift
index b1fde05..9f07dcd 100644
--- a/Sources/DataStructures/ContiguousSegmentCollection/ContiguousSegmentCollection.swift
+++ b/Sources/DataStructures/ContiguousSegmentCollection/ContiguousSegmentCollection.swift
@@ -527,3 +527,4 @@ extension ContiguousSegmentCollection: CustomStringConvertible {
 
 extension ContiguousSegmentCollection: Equatable where Segment: Equatable { }
 extension ContiguousSegmentCollection: Hashable where Segment: Hashable { }
+extension ContiguousSegmentCollection: Codable where Metric: Codable, Segment: Codable { }
diff --git a/Sources/DataStructures/Either.swift b/Sources/DataStructures/Either.swift
index 5eccd5d..8757621 100644
--- a/Sources/DataStructures/Either.swift
+++ b/Sources/DataStructures/Either.swift
@@ -45,5 +45,38 @@ public enum Either <Left,Right> {
     }
 }
 
+extension Either: Codable where Left: Codable, Right: Codable {
+
+    enum DecodingError: Error {
+        case invalidCase
+    }
+
+    enum CodingKeys: String, CodingKey {
+        case left
+        case right
+    }
+
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        if let value = try? container.decode(Left.self, forKey: .left) {
+            self = .left(value)
+        } else if let value = try? container.decode(Right.self, forKey: .right) {
+            self = .right(value)
+        } else {
+            throw DecodingError.invalidCase
+        }
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        switch self {
+        case let .left(value):
+            try container.encode(value, forKey: .left)
+        case let .right(value):
+            try container.encode(value, forKey: .right)
+        }
+    }
+}
+
 extension Either: Equatable where Left: Equatable, Right: Equatable { }
 extension Either: Hashable where Left: Hashable, Right: Hashable { }
diff --git a/Sources/DataStructures/IntervalRelation.swift b/Sources/DataStructures/IntervalRelation.swift
index ab6aa4d..00e2b1e 100644
--- a/Sources/DataStructures/IntervalRelation.swift
+++ b/Sources/DataStructures/IntervalRelation.swift
@@ -24,7 +24,7 @@
 /// [Allen](https://en.wikipedia.org/wiki/James_F._Allen), refined by
 /// [Krokhin et al.](http://www.ics.uci.edu/~alspaugh/cls/shr/allen.html#Allen1983-mkti).
 ///
-public enum IntervalRelation: InvertibleEnum {
+public enum IntervalRelation: String, InvertibleEnum {
 
     // MARK: - Cases
 
@@ -164,3 +164,4 @@ extension RangeProtocol {
 
 extension IntervalRelation: Equatable { }
 extension IntervalRelation: Hashable { }
+extension IntervalRelation: Codable { }
diff --git a/Sources/DataStructures/LinkedList.swift b/Sources/DataStructures/LinkedList.swift
index c792021..c36744e 100644
--- a/Sources/DataStructures/LinkedList.swift
+++ b/Sources/DataStructures/LinkedList.swift
@@ -101,3 +101,5 @@ extension LinkedList: ExpressibleByArrayLiteral {
 
 extension LinkedList: Equatable where Element: Equatable { }
 extension LinkedList: Hashable where Element: Hashable { }
+
+// TODO: Codable
diff --git a/Sources/DataStructures/Matrix.swift b/Sources/DataStructures/Matrix.swift
index 6dcd21b..629c796 100644
--- a/Sources/DataStructures/Matrix.swift
+++ b/Sources/DataStructures/Matrix.swift
@@ -156,3 +156,4 @@ extension Matrix: CustomStringConvertible {
 
 extension Matrix: Equatable where Element: Equatable { }
 extension Matrix: Hashable where Element: Hashable { }
+extension Matrix: Codable where Element: Codable { }
diff --git a/Sources/DataStructures/OrderedDictionary.swift b/Sources/DataStructures/OrderedDictionary.swift
index fff7ea1..0ca183c 100644
--- a/Sources/DataStructures/OrderedDictionary.swift
+++ b/Sources/DataStructures/OrderedDictionary.swift
@@ -134,3 +134,4 @@ extension OrderedDictionary: ExpressibleByDictionaryLiteral {
 
 extension OrderedDictionary: Equatable where Value: Equatable { }
 extension OrderedDictionary: Hashable where Value: Hashable { }
+extension OrderedDictionary: Codable where Key: Codable, Value: Codable { }
diff --git a/Sources/DataStructures/Pair/UnorderedPair.swift b/Sources/DataStructures/Pair/UnorderedPair.swift
index 93d4f07..e4a65a0 100644
--- a/Sources/DataStructures/Pair/UnorderedPair.swift
+++ b/Sources/DataStructures/Pair/UnorderedPair.swift
@@ -59,8 +59,6 @@ extension UnorderedPair: Hashable where T: Hashable {
     }
 }
 
-extension UnorderedPair: Codable where T: Codable { }
-
 extension UnorderedPair: CustomStringConvertible {
 
     // MARK: - CustomStringConvertible
@@ -70,3 +68,5 @@ extension UnorderedPair: CustomStringConvertible {
         return "{\(a),\(b)}"
     }
 }
+
+extension UnorderedPair: Codable where T: Codable { }
diff --git a/Sources/DataStructures/Queue.swift b/Sources/DataStructures/Queue.swift
index ac472e3..a2b28e5 100644
--- a/Sources/DataStructures/Queue.swift
+++ b/Sources/DataStructures/Queue.swift
@@ -72,3 +72,4 @@ extension Queue {
 
 extension Queue: Equatable where Element: Equatable { }
 extension Queue: Hashable where Element: Hashable { }
+extension Queue: Codable where Element: Codable { }
diff --git a/Sources/DataStructures/SortedArray.swift b/Sources/DataStructures/SortedArray.swift
index aa580c9..48d5d92 100644
--- a/Sources/DataStructures/SortedArray.swift
+++ b/Sources/DataStructures/SortedArray.swift
@@ -172,3 +172,4 @@ extension SortedArray: ExpressibleByArrayLiteral {
 
 extension SortedArray: Equatable { }
 extension SortedArray: Hashable where Element: Hashable { }
+extension SortedArray: Codable where Element: Codable { }
diff --git a/Sources/DataStructures/SortedDictionary.swift b/Sources/DataStructures/SortedDictionary.swift
index 70b32e1..e9a0698 100644
--- a/Sources/DataStructures/SortedDictionary.swift
+++ b/Sources/DataStructures/SortedDictionary.swift
@@ -205,3 +205,4 @@ extension SortedDictionary: Zero {
 
 extension SortedDictionary: Equatable where Value: Equatable { }
 extension SortedDictionary: Hashable where Value: Hashable { }
+extension SortedDictionary: Codable where Key: Codable, Value: Codable { }
diff --git a/Sources/DataStructures/Stack.swift b/Sources/DataStructures/Stack.swift
index 35d69c7..c2c944d 100644
--- a/Sources/DataStructures/Stack.swift
+++ b/Sources/DataStructures/Stack.swift
@@ -168,3 +168,4 @@ extension Stack: Monoid {
 
 extension Stack: Equatable where Element: Equatable { }
 extension Stack: Hashable where Element: Hashable { }
+extension Stack: Codable where Element: Codable { }
diff --git a/Sources/DataStructures/Tree.swift b/Sources/DataStructures/Tree.swift
index 1fce4f8..5909eb2 100644
--- a/Sources/DataStructures/Tree.swift
+++ b/Sources/DataStructures/Tree.swift
@@ -368,3 +368,5 @@ public func zip <T,U,V> (_ a: Tree<T,T>, _ b: Tree<U,U>, _ f: (T, U) -> V) -> Tr
 
 extension Tree: Equatable where Leaf: Equatable, Branch: Equatable { }
 extension Tree: Hashable where Leaf: Hashable, Branch: Hashable { }
+
+// TODO: Codable