Analyses of two-particle correlations have provided the chief means for
determining spatio-temporal characteristics of relativistic heavy ion
collisions. We discuss the theoretical formalism behind these studies and the
experimental methods used in carrying them out. Recent results from RHIC are
put into context in a systematic review of correlation measurements performed
over the past two decades. The current understanding of these results is
discussed in terms of model comparisons and overall trends.Comment: 49 pages, 16 figures; to appear in Annual Review of Nuclear and
Particle Science; final version includes minor updates in text, a few
references added, and two figures updated; Figures and numerical data tables
available at http://www.physics.ohio-state.edu/~lisa/FemtoscopyReview2005