The geometry of the 2/2 twill is studied by reference to (a) an idealized cloth made of flexible and frictionless threads, and (b) a simpler model derived from this. The existence of interactions tending to disturb the model from a square configuration is shown and their magnitudes are related to the basic parameters. In the idealized cloth, these interactions produce an equilibrium configuration which is not square. The degree of skewness is related to the diameter and crimp of the threads and the influence of yarn stiffness and friction on the skewness in practical cloths is discussed.