In chess, the fianchetto (English: /ˌfiənˈkɛtoʊ/ or /ˌfiənˈtʃɛtoʊ/; Italian:"little flank") is a pattern of development wherein a bishop is developed to the second rank of the adjacent b- or g-file, the knight pawn having been moved one or two squares forward.

The fianchetto is a staple of many "hypermodern" openings, whose philosophy is to delay direct occupation of the centre with the plan of undermining and destroying the opponent's occupied centre. It also regularly occurs in Indian defences. The fianchetto is less common in Open Games (1.e4 e5), but the king bishop is sometimes fianchettoed by Black in the Ruy Lopez or by White in an uncommon variation of the Vienna Game.

One of the major benefits of the fianchetto is that it often allows the fianchettoed bishop to become more active. A fianchettoed position, however, also presents some opportunities for the opponent: if the fianchettoed bishop can be exchanged, the squares the bishop was formerly protecting will become weak (see hole) and can form the basis of an attack (particularly if the fianchetto was performed on the kingside). Exchanging the fianchettoed bishop should not be done lightly, therefore, especially if the enemy bishop on same-coloured squares is still on the board.
What is the main benefit of the fianchetto in chess openings?
The fianchetto follows the "hypermodern" opening philosophy. It lets a bishop become more active from the flanks, attacking the center of the board without directly occupying it.