The Sunyaev-Zel'dovich Effect and its Uses

After briefly recalling the physics of the thermal and kinetic Sunyaev-Zel'dovich effects, I review some recent results and discuss future directions. Present achievements include the construction of Hubble diagrams and measurements of baryon fractions with catalogs consisting of tens of clusters, leading to reasonable constraints on the Hubble constant and the matter density. Detailed millimeter spectra and corresponding peculiar velocity limits have been obtained for ～ 10 clusters. A new generation of instruments based on interferometer arrays and bolometer cameras will soon open the way to SZ surveying, and near the turn of the decade the Planck mission will provide an almost all-sky catalog of more than 10,000 clusters distributed out to redshifts beyond unity. I finish with a discussion of several aspects of surveying and of the science targeted by these projects.