We present an introduction to the subjects of emittance and space‐charge effects in charged‐particle beams. This is followed by a discussion of three important topics that are at the frontier of this field. The first is a simple model, describing space‐charge‐induced emittance growth, which yields scaling formulas and some physical explanations for some of the surprising results. The second is a discussion of beam halo, an introduction to the particle‐core model, and a brief summary of its results. The third topic is an introduction to the hypothesis of equipartitioning for collisionless particle beams. ©1996 American Institute of Physics.