In a max-min LP, the objective is to maximise subject to Ax 1, Cx 1, and x 0 for nonnegative matrices A and C. We present a local algorithm (constant-time distributed algorithm) for approximating max-min LPs. The approximation ratio of our algorithm is the best possible for any local algorithm; there is a matching unconditional lower bound. Categories and Subject Descriptors C.2.4 [Computer-Communication Networks]: Distrib