Anderssen's Opening is an irregular chess opening defined by the move 1.a3. ECO code: A00.

History

The opening is named after Adolf Anderssen (1818–1879), the dominant chess player of the mid-19th century, renowned for the "Immortal Game" and the "Evergreen Game." Anderssen occasionally employed 1.a3, though it was never a principal weapon in his repertoire.

Main Lines & Variations

The move 1.a3 makes a minimal pawn advance on the queenside, doing nothing for central control or piece development. Its only concrete purpose is to prevent ...Bb4 or ...Nb4 in certain future positions and to prepare a possible b4 advance. Black responds most effectively with natural central occupation: 1...e5, 1...d5, or 1...Nf6.

Strategic Themes & Plans

White essentially cedes the first-move advantage, waiting to see Black's setup before committing to a plan. The pawn on a3 can prove useful later in certain structures—it prevents piece incursions to b4 and supports a future b4 expansion. However, these benefits do not compensate for the loss of tempo. The opening can transpose into reversed versions of various Black defences once White plays e4 or d4 on a subsequent move. It is considered one of the weakest first moves and appears only occasionally as a surprise or psychological weapon.