The instability of present theory to describe correctly the shoaling transformation of surface gravity waves is well recognized. It owes, at least in part, to the lack of experimental information on internal flow fields. This paper describes a portion of the results from laboratory experiments in which the time histories of surface elevation, crest speed, and horizontal subsurface flow velocities in trains of uniform waves were measured at a plurality of stations before and after breaking, as functions of (uniform) beach slope and wave frequency. It was found that over gentle slopes, wave breaking is characterized by invariancy of crest profiles and kinematics and that most important breaking parameters can be expressed in terms of period and breaker height, the latter of which appears to be related simply to deepwater height and steepness.