The main results of experimental and theoretical investigations on the pressure-induced infrared absorption of nonpolar molecules are outlined, with particular emphasis on those properties which may be of importance in studies of planetary atmospheres containing hydrogen and helium. The structures of the fundamental and overtone absorptions of hydrogen are explained in some detail, and a possible explanation for the frequency discrepancy of the planetary S3(0) and S4 (0) features is given. Our present knowledge of the shape of the high frequency wing in induced absorption is reviewed. Abstract The main results of experimental and theoretical investigations on the pressure-induced infrared absorption of nonpolar molecules are outlined, with particular emphasis on those properties which may be of importance in studies of planetary atmospheres containing hydrogen and helium. The structures of the fundamental and overtone absorptions of hydrogen are explained in some detail, and a possible explanation for the frequency discrepancy of the planetary S3(0) and S4 (0) features is given. Our present knowledge of the shape of the high frequency wing in induced absorption is reviewed.