Abstract
The state of the current understanding of hydrogen in elemental and compound semiconductors is reviewed. The results of new experimental and theoretical studies of the microscopic structure of acceptor-hydrogen and donor-hydrogen complexes are presented. Questions regarding hydrogen tunnelling in some of the acceptor and donor complexes in elemental semiconductors, as well as the problem of electronic states of isolated hydrogen, are discussed in the light of the most recent experimental findings. Also, some promising areas of future research are indicated.