This is the 4th expansion to the game of Dominion. It adds 25 new Kingdom cards to Dominion, plus 2 new Basic cards that let players keep building up past Gold and Province. The central theme is wealth; there are treasures with abilities, cards that interact with treasures, and powerful expensive cards.
Dominion: Prosperity is an expansion to Dominion. Thus, Dominion: Prosperity cannot be played by itself; to play with it, you need the Basic cards (Treasure, Victory, and Curse cards), and the full rules for setup and gameplay (Dominion provides both).