Anderssen's Opening is a defined by the opening move

1. a3.

It is named after unofficial World Chess Champion Adolf Anderssen, who played it three times in his 1858 match against Paul Morphy. While Anderssen was defeated decisively, the games he opened with this novelty scored 1.5/3.0 (1 win, 1 loss, 1 draw).

This opening move does little for development or control of the center. In some cases, White can transpose the game to an opening where 1.a3 might have been useful, but using a tempo on such a move already on move one seems premature. As Anderssen's Opening is not commonly played, it is considered an irregular opening. The move is classified under the A00 code in the Encyclopaedia of Chess Openings.

Anderssen's Opening is not a very constructive move for White, more a waiting move. However, some players may enjoy the psychological value of such a move, or believe it will help them against an opponent with a superior knowledge of opening theory.

Among the more common Black responses to Anderssen's Opening are 1...d5, which makes a straightforward claim of the center; and 1...g6, which prepares to fianchetto the bishop to g7 as developing the bishop to b4 is unlikely and from g7 it puts pressure on the slightly weakened queenside squares. The response 1...e5 is also possible, but White can then play 2.c4, leading to a kind of Sicilian Defence with colors reversed, where a pawn on a3 can be useful. Another approach is 2.e4 Nf6 3.Nc3, transposing to Mengarini's Opening.

A modern proponent of the move is Croatian International master Dr. Zvonko Krecak.