A flank opening is any game where White does not begin with 1.P-K4 or 1.P-Q4, but instead opens with another piece and aims to control the centre by indirect play. Most are easily transposeable into one or another of the main KP or QP Opening variations.

The chief flank openings are the English Opg. (qv.) (seen left, with Black's main reply) and the Zuckertort (seen right with reply, usually becoming a Reti Opg. (qv.) or an Indian Defence (qv.) by transposition).

Other flank openings are termed irregular (being rarely seen in master play). They include Bird's Opening (qv.), Larsen's Opening, the King's Fianchetto Opening and the Nimzowitsch Opening. Also the Grob (or Spike), Van't Kruys and the Saragossa.