diff --git a/.releases/4.47.0.md b/.releases/4.47.0.md
new file mode 100644
index 0000000..429bbf5
--- /dev/null
+++ b/.releases/4.47.0.md
@@ -0,0 +1,3 @@
+**New Features**
+
+* Added an optional numeric `mapping` value to the `Enum` class (used when external systems identify enumeration items with integer values). This change is backwards compatible.
\ No newline at end of file
diff --git a/lang/Enum.js b/lang/Enum.js
index 85f446a..292e5b7 100644
--- a/lang/Enum.js
+++ b/lang/Enum.js
@@ -1,4 +1,5 @@
-const assert = require('./assert');
+const assert = require('./assert'),
+	is = require('./is');
 
 module.exports = (() => {
 	'use strict';
@@ -14,24 +15,32 @@ module.exports = (() => {
 	 * @interface
 	 * @param {String} code - The unique code of the enumeration item.
 	 * @param {String} description - A description of the enumeration item.
+	 * @param {Number=} mapping - An alternate key value (used when external systems identify enumeration items using integer values).
 	 */
 	class Enum {
-		constructor(code, description) {
+		constructor(code, description, mapping) {
 			assert.argumentIsRequired(code, 'code', String);
 			assert.argumentIsRequired(description, 'description', String);
+			assert.argumentIsOptional(mapping, 'mapping', Number);
+
+			if (is.number(mapping)) {
+				assert.argumentIsValid(mapping, 'mapping', is.integer, 'must be an integer');
+			}
 
 			this._code = code;
 			this._description = description;
 
+			this._mapping = mapping || null;
+
 			const c = this.constructor;
 
 			if (!types.has(c)) {
 				types.set(c, [ ]);
 			}
 
-			const existing = Enum.fromCode(c, code);
+			const valid = Enum.fromCode(c, this._code) === null && (this._mapping === null || Enum.fromMapping(c, this._mapping) === null);
 
-			if (existing === null) {
+			if (valid) {
 				types.get(c).push(this);
 			}
 		}
@@ -56,6 +65,17 @@ module.exports = (() => {
 			return this._description;
 		}
 
+		/**
+		 * An alternate key value (used when external systems identify enumeration items
+		 * using numeric values). This value will not be present for all enumerations.
+		 *
+		 * @public
+		 * @returns {Number|null}
+		 */
+		get mapping() {
+			return this._mapping;
+		}
+
 		/**
 		 * Returns true if the provided {@link Enum} argument is equal
 		 * to the instance.
@@ -86,14 +106,32 @@ module.exports = (() => {
 		 * @static
 		 * @param {Function} type - The enumeration type.
 		 * @param {String} code - The enumeration item's code.
-		 * @returns {*|null}
+		 * @returns {Enum|null}
 		 */
 		static fromCode(type, code) {
 			return Enum.getItems(type).find(x => x.code === code) || null;
 		}
 
 		/**
-		 * Returns all of the enumeration's items (given an enumeration type).
+		 * Looks up a enumeration item; given the enumeration type and the enumeration
+		 * item's value. If no matching item can be found, a null value is returned.
+		 *
+		 * @public
+		 * @static
+		 * @param {Function} type - The enumeration type.
+		 * @param {String} mapping - The enumeration item's mapping value.
+		 * @returns {Enum|null}
+		 */
+		static fromMapping(type, mapping) {
+			if (mapping === null) {
+				return null;
+			}
+
+			return Enum.getItems(type).find(x => x.mapping === mapping) || null;
+		}
+
+		/**
+		 * Returns the enumeration's items (given an enumeration type).
 		 *
 		 * @public
 		 * @static
diff --git a/test/specs/lang/EnumSpec.js b/test/specs/lang/EnumSpec.js
index 9665262..f1cdfba 100644
--- a/test/specs/lang/EnumSpec.js
+++ b/test/specs/lang/EnumSpec.js
@@ -37,14 +37,75 @@ describe('When Enum is extended (as types EnumA and EnumB) and type items are ad
 	});
 
 	describe('and a duplicate item (A-x) is added', () => {
-		let axx = new EnumA('x', 'A-XX');
+		let invalid = new EnumA('x', 'A-XX');
 
-		it('should be still find the original instance in EnumA for X', () => {
+		it('should still only have two items', () => {
+			expect(Enum.getItems(EnumA).length).toEqual(2);
+		});
+
+		it('should still able to find the original instance in EnumA for X', () => {
 			expect(Enum.fromCode(EnumA, 'x')).toBe(ax);
 		});
 
+		it('should not be able to find the mapping for the duplicated item', () => {
+			expect(Enum.getItems(EnumA).some(x => x === invalid)).toEqual(false);
+		});
+
 		it('should should equal the original instance (for X)', () => {
-			expect(Enum.fromCode(EnumA, 'x').equals(axx)).toBe(true);
+			expect(Enum.fromCode(EnumA, 'x').equals(ax)).toBe(true);
+		});
+	});
+});
+
+describe('When Enum is extended (as types EnumA and EnumB) and type items are added to each (X and Y) which include mapping values', () => {
+	'use strict';
+
+	class EnumA extends Enum {
+		constructor(code, description, mapping) {
+			super(code, description, mapping);
+		}
+	}
+
+	class EnumB extends Enum {
+		constructor(code, description, mapping) {
+			super(code, description, mapping);
+		}
+	}
+
+	let ax = new EnumA('x', 'A-X', 1);
+	let ay = new EnumA('y', 'A-Y', 2);
+	let bx = new EnumB('x', 'B-X', 1);
+	let by = new EnumB('y', 'B-Y', 2);
+
+	it('should be able to find X in EnumA using the mapping value', () => {
+		expect(Enum.fromMapping(EnumA, 1)).toBe(ax);
+	});
+
+	it('should be able to find Y in EnumA using the mapping value', () => {
+		expect(Enum.fromMapping(EnumA, 2)).toBe(ay);
+	});
+
+	it('should be able to find X in EnumB using the mapping value', () => {
+		expect(Enum.fromMapping(EnumB, 1)).toBe(bx);
+	});
+
+	it('should be able to find Y in EnumB using the mapping value', () => {
+		expect(Enum.fromMapping(EnumB, 2)).toBe(by);
+	});
+
+	describe('and a duplicate mapping value is added', () => {
+		let invalid = new EnumA('z', 'A-Z', 2);
+
+		it('should still only have two items', () => {
+			expect(Enum.getItems(EnumA).length).toEqual(2);
+		});
+
+		it('should still able to find the original instance in EnumA for Y', () => {
+			expect(Enum.fromMapping(EnumA, 2)).toBe(ay);
+		});
+
+		it('should not be able to find the mapping for the duplicated item', () => {
+			expect(Enum.getItems(EnumA).some(x => x === invalid)).toEqual(false);
 		});
 	});
 });
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