The square flap method refers to the modified three-flap Z-plasty that combines one square-advancement flap with two triangular transposed flaps. It is mainly used to reconstruct single linear or band scar contractures in web spaces such as the axilla and elbow, but can also be used to correct clefts, cryptotia, and epicanthal folds. Its function is to increase the length between two points on the skin surface (i.e., the commissure) by up to 2.825-fold. This greatly reduces the biomechanical skin tension on the scar, which in turn decreases postsurgical recurrence. Moreover, the commissure is not only lengthened by the square flap; it also forms a three-dimensional trough that is sufficiently deep and wide and has the required shape. The square flap method offers superior lengthening capacity and restoration of function and aesthetics compared to the single-, four-, and five-flap Z-plasties. It also does not divide the hairy regions in the axilla, thus futhre promoting good aesthetics. Thus, the square flap achieves good outcomes without requiring skin excisions.