--- title: "Opening theory in chess" url: "https://georgelichess.com/glossary/opening-theory.md" canonical_url: "https://georgelichess.com/glossary/opening-theory" last_updated: "2026-11-07" type: "reference" summary: "Opening theory is the body of knowledge about the opening, made up of the known moves. Theory is organized by opening and variation." related: ["https://georgelichess.com/glossary/opening.md", "https://georgelichess.com/glossary/opening-preparation.md", "https://georgelichess.com/glossary/novelty.md", "https://georgelichess.com/glossary/main-line.md", "https://georgelichess.com/glossary/book-move.md", "https://georgelichess.com/glossary/out-of-book.md", "https://georgelichess.com/glossary/category/opening-concepts.md", "https://georgelichess.com/glossary.md"] --- # Opening theory in chess > **For AI agents:** the complete index of GeorgeLiChess pages is [llms.txt](https://georgelichess.com/llms.txt). Every page is also served as markdown at its URL plus .md. Opening theory is the body of knowledge about the opening, made up of the known moves. Theory is organized by opening and variation. Opening theory is the body of knowledge about the opening, made up of the known moves, plans and evaluations of the main lines that players have tested over many games. [Opening](https://georgelichess.com/glossary/opening.md) theory is the collected knowledge about how the first moves are best played. It comes from centuries of practice and analysis, and today [engines](https://georgelichess.com/glossary/chess-engine.md) and [databases](https://georgelichess.com/glossary/database.md) extend it. It records which moves are considered best, which lines are risky and what plans each structure suits. Theory is organized by opening and variation. A [main line](https://georgelichess.com/glossary/main-line.md) is the most tested path, and [sidelines](https://georgelichess.com/glossary/sideline.md) are less common choices. In some lines, theory runs more than twenty moves deep, and the two players may both know it to the end. In others, it stops after a few moves, and you are on your own. Knowing theory helps in two ways. It saves time and avoids early [mistakes](https://georgelichess.com/glossary/mistake.md), and it shows typical pawn structures and plans. The second use matters more for most players. A move you recognize is a good starting point, but understanding why it is played is what lets you keep going when theory ends. Theory changes. A line that was strong years ago may be refuted by a new idea, and a forgotten line may come back. A common mistake is to treat theory as fixed, or to learn only moves. Study the games that illustrate the line, and check where the main games turn from theory to original play. Also called: theory. A neighboring idea is [Book move](https://georgelichess.com/glossary/book-move.md). A book move is a move in a well established opening line, one that already appears in published analysis, opening databases or an engine's prepared opening list, so a player can choose it from knowledge rather than calculation. Also worth reading is [Opening explorer](https://georgelichess.com/glossary/opening-explorer.md). An opening explorer is a tool that shows, for any position reached from the start, which moves players have chosen in past games and how often each move led to a win, draw or loss. Also worth reading is [Tabiya](https://georgelichess.com/glossary/tabiya.md). A tabiya is a standard, well known position that arises in a particular opening after a sequence of typical moves, and from which the main plans and ideas of both sides are understood. Opening ideas such as "Opening theory" are easier to keep when they are tested on your own games, which is what a [first lesson](https://georgelichess.com/book/first-lesson.md) with George Li begins with. ## Related terms - [Opening](https://georgelichess.com/glossary/opening.md) - [Opening preparation](https://georgelichess.com/glossary/opening-preparation.md) - [Novelty](https://georgelichess.com/glossary/novelty.md) - [Main line](https://georgelichess.com/glossary/main-line.md) - [Book move](https://georgelichess.com/glossary/book-move.md) - [Out of book](https://georgelichess.com/glossary/out-of-book.md) ## Guides that go further - [Most popular chess openings and win rates](https://georgelichess.com/chess-opening-statistics.md): The most played openings, how often White wins, and how the numbers change with rating, computed from public games. - [How to choose a chess coach](https://georgelichess.com/how-to-choose-a-chess-coach.md): What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid. - [The first lesson](https://georgelichess.com/book/first-lesson.md): A game review, a read on your level and a written study plan from George Li. [Book your first lesson](https://georgelichess.com/book.md) and George Li reviews your games and builds a study plan around them. Questions about lessons: write to hello@georgelichess.com. ## Related - [Opening in chess](https://georgelichess.com/glossary/opening.md) - [Opening preparation in chess](https://georgelichess.com/glossary/opening-preparation.md) - [Novelty in chess](https://georgelichess.com/glossary/novelty.md) - [Main line in chess](https://georgelichess.com/glossary/main-line.md) - [Book move in chess](https://georgelichess.com/glossary/book-move.md) - [Out of book in chess](https://georgelichess.com/glossary/out-of-book.md) - [Chess terms: Opening concepts](https://georgelichess.com/glossary/category/opening-concepts.md) - [Chess terms glossary: plain definitions](https://georgelichess.com/glossary.md)