Developments in water gas shift (WGS) catalysis, especially during the last decade, are reviewed. Recent developments include the development of 1 chromium-free catalysts that can operate at lower steam to gas ratios and 2 more active catalysts that can operate at gas hourly space velocities above 40,000h-1. A current challenge is to develop catalysts for use in fuel cell applications. Precious metal catalysts supported on partially reducible oxide supports (Pt-ceria, Pt-titania, Au-ceria, etc.) are the current front runners. A critical review of the mechanism of the WGS reaction is also presented.