This is an announcement for the paper "Differentiability of Lipschitz maps from metric measure spaces to Banach spaces with the Radon Nikodym property" by Jeff Cheeger and Bruce Kleiner. Abstract: We prove the differentiability of Lipschitz maps X---->V, where X is a complete metric measure space satisfying a doubling condition and a Poincar\'e inequality, and V is a Banach space with the Radon Nikodym Property (RNP). The proof depends on a new characterization of the differentiable structure on such metric measure spaces, in terms of directional derivatives in the direction of tangent vectors to suitable rectifiable curves. Archive classification: math.MG math.DG math.FA Mathematics Subject Classification: 46B22 (primary), 46G05 (secondary) The source file(s), pirnp.bbl: 3004 bytes The paper may be downloaded from the archive by web browser from URL http://front.math.ucdavis.edu/0808.3249 or http://arXiv.org/abs/0808.3249 or by email in unzipped form by transmitting an empty message with subject line uget 0808.3249 or in gzipped form by using subject line get 0808.3249 to: math@arXiv.org.