The search for protostellar inflow

Very few protostellar clouds show direct evidence for infall. This review discusses the plausibility of the detection of infall in the context of both dynamic and quasi-static (magnetic) collapse models. The search for infall has been based on the study of spectral energy distributions (which form the basis of the protostellar classification scheme), the relative spatial distribution of molecular material and the analysis of spectral line profiles. Only the latter method gives direct evidence for velocity structure and the presence of inflow. The interpretation of line profiles is complicated by chemical effects but, with a self-consistent approach to the modelling, powerful diagnostics of the infall dynamics may be obtained.