Provides are crystalline forms of nateglinide, labeled Forms A, C, D, F, G, I, J, K, L, M, N, O, P, Q, T, U, V, Y, .alpha., .beta., .gamma., .delta., .epsilon., .sigma., .theta. and .OMEGA., processes for their preparation and processes for preparation of other crystalline forms of nateglinide. Also provided are their pharmaceutical formulations and methods of administration.