Study of molecular gas in distant galaxies during the last twenty years has followed the steady progress in mm wave receiver sensitivity. In 1975, CO was detected in M 82, NGC 253, and several other galaxies with redshifts of a few hundred kms−1 (Rickard et al. 1975; Solomon & de Zafra 1975). Over the next fifteen years, the CO detection horizon increased steadily, reaching z ≈ 0.22 by 1990 (Downes et al. 1991). The discovery that the large population of infrared luminous galaxies detected by IRAS are very gas rich (e.g., Sanders, Scoville, & Soifer 1991) was especially significant. In the last few years, CO has been detected in two high redshift objects, IRAS FSC 10214+4724 at z = 2.3 (Brown & Vanden Bout 1992b) and the Cloverleaf quasar (H1413+117) at z = 2.6 (Barvainis et al. 1994; Barvainis 1996). These objects offer glimpses of galaxies’ properties when the Universe was only about 15% of its present age. The presence and conditions of molecular gas in galaxies at such an early epoch are clues to understanding galaxy formation and evolution in the early Universe.