Book move
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 called: in book
The name goes back to printed opening manuals, the books players once carried to tournaments. Today the same idea covers databases of master games and the opening files that chess engines use, which let a program answer the first moves instantly instead of searching.
The phrase in book describes a game in which nothing new has happened yet. The first unfamiliar position takes it out of book, and from then on both players are thinking for themselves.
A book move saves clock time and avoids early accidents, because its consequences have been tested in many games. It is not automatically right for you, though. Some book moves lead to positions that suit a different style, and a move that is standard in one move order can be a mistake in another. Knowing why the move is played matters as much as knowing that it is played.
A habit worth breaking is replying instantly with the usual book move when the opponent has just done something slightly different. A small change earlier in the game can turn the familiar reply into a blunder, so look at the actual position before reaching for the move you remember.
It sits close to Novelty. A novelty is a move that has not been played before in a known position of an opening, introduced to take the opponent out of their preparation and into unexplored territory.
Compare it with Opening book. An opening book is a database of opening moves and positions that an engine or program consults to play known theory quickly, instead of calculating each early move from scratch.
It sits close to Transposition. A transposition is a change of route, most often in the opening: the moves come in an unusual order, yet the board ends up in a position normally associated with another order or even another opening.
Whether "Book move" suits your repertoire depends on the games you play. A first lesson with George Li maps what you play today and what to build next.
Related terms
A player is out of book when the game reaches a position that neither side is recalling from opening knowledge or preparation, so from that move on the choices have to be worked out at the board.
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.
A novelty is a move that has not been played before in a known position of an opening, introduced to take the opponent out of their preparation and into unexplored territory.
The main line is the sequence of moves most often played in an opening, the one considered the most critical test, and the one that theory has analyzed in the greatest depth.
An opening book is a database of opening moves and positions that an engine or program consults to play known theory quickly, instead of calculating each early move from scratch.
Move order is the sequence in which moves are played to reach a given setup, and it matters because the same final position can allow the opponent different choices depending on which move comes first.
Guides that go further
Most popular chess openings and win rates
The most played openings, how often White wins, and how the numbers change with rating, computed from public games.
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.