Published in "The Extragalactic Distance Scale", Space Telescope Science Institute Symposium Series 10, 1997, eds. M. Livio, M. Donahue and N. Panagia

Abstract. The Cosmic Microwave Background is a powerful tool with which to constrain cosmological parameters. In this contribution we review the way in which the Sunyaev-Zel'dovich effect in clusters can be used to find a value for H₀ that is independent of the usual distance-scale assumptions. New values of H₀ obtained using the Ryle Telescope at Cambridge and other telescopes are discussed, with special emphasis on the systematic effects that may be present in the method. The use of the power spectrum of primordial microwave background fluctuations to constrain H₀ is then discussed, and illustrated in connection with the current experimental results for background anisotropy.

Table of Contents

• INTRODUCTION
• THE SZ EFFECT
• RYLE TELESCOPE H₀ RESULTS AND ERRORS
• DETECTION OF A MICROWAVE DIMINUTION TOWARDS A HIGH-Z QUASAR PAIR
• OTHER SZ DETERMINATIONS OF H₀
• USING PRIMORDIAL ANISOTROPIES TO CONSTRAIN H₀
• REFERENCES