[en] Since the pioneering work of Cherry the subject of slow positrons has been intimately connected with surfaces. The relatively high yield slow positron source of Canter et al. permitted subsequent studies in ultra-high vacuum which have given some understanding of how positrons interact with surfaces. This knowledge has enabled better slow positron moderators yielding higher beam strengths for experimentation on surfaces and solids and for studying positronium and positron-molecule scattering at low energies to be made. The present knowledge of positron and positronium work functions, the positron surface state, positron stopping and positron diffusion are reviewed. The paper concludes with a brief speculation about the experimental possibilities offered by future slow positron beams of high flux and brightness. (0uth.)