Age of Empires II: The Age of Kings (often shortened to The Age of Kings or AoK) is a real-time strategy (RTS) video game developed by Ensemble Studios and published by Microsoft. Released on September 30, 1999 for the Microsoft Windows and Macintosh operating systems, it was the second game in the Age of Empires series. An expansion, The Conquerors, was released in 2000. A PlayStation 2 version was released by Konami in 2001, and a Nintendo DS spinoff, Age of Empires: The Age of Kings was developed by Backbone Entertainment in 2006.

The Age of Kings is set in the Middle Ages and contains thirteen playable civilizations. Players aim to gather resources, which they use to build towns, create armies, and ultimately defeat their enemies. There are five historically-based campaigns, which constrict the player to specialized and story-backed conditions. There are three additional single player game modes, and multiplayer is supported. Despite using the same game engine and similar code to its predecessor, development of The Age of Kings took a year longer than expected, forcing Ensemble Studios to release Age of Empires: The Rise of Rome in 1998 instead. The design team focused on resolving significant issues in Age of Empires, but noted on release that some problems remained.