In short: What is known and analyzed about the openings: which moves are played, where they lead and who stands better afterward.
Opening theory is everything that has been played, analyzed and written about the openings, move by move. For every known position there are answers to the questions: which moves are played here, where do they lead, and who stands better afterward? Whoever knows the theory recognizes the positions and knows what usually happens.
How deep does theory go?
In the most important openings, theory reaches up to about 20 moves, and in a few sharp lines 30 to 35 moves. When you are no longer following anything that has been played before, you have left theory. Then you have to think for yourself.
Five hundred years of theory
Opening theory goes back to the end of the 1400s, when the rules had taken their modern form and players began to study the openings. Luis Ramírez de Lucena's book of 1497 is the oldest surviving printed book on how to play. In the 1800s the study became systematic, and the Handbuch des Schachspiels of 1843 was long the most important reference work.
Theory is still growing. Before important matches, strong players look for new moves their opponents haven't seen. Such a move is called a novelty.
How much do you need to know?
As a beginner, almost nothing. Learn the ideas instead: take space in the center, get the pieces out and castle. If you understand why the moves are played, you remember them more easily, and you cope better when your opponent does something unexpected. Start with our chess openings, where each opening is explained move by move, and read how the openings are divided into variations and ECO codes.
Frequently asked questions
How deep does theory go?
In the most important openings up to about 20 moves, and in a few lines 30 to 35 moves.
How much theory does a beginner need?
Almost none. Learn the ideas instead: the center, development and castling. Theory becomes useful once you understand why the moves are played.
Updated November 14, 2026