A review of the current status of research on Er3+ doped hydrogenated amorphous silicon (a-Si:H) is presented. Er has been introduced in a-Si:H and a-SiOx:H by ion implantation, co-sputtering and PECVD. In all cases, the characteristic atomic-like intra-4f I-4(13/2) --> I-4(15/2) photoluminescence emission at similar to 1.54 mu m is observed at room temperature. The Er3+ luminescence probability is determined by the local neighborhood of the ions. Therefore, local probes like EXAFS and Mossbauer spectroscopy have yielded very important information. A discussion of excitation processes, electroluminescence, and electronic doping effects, is also presented.294616622