Although the kinematics, mechanics, energetics and mathematics of trot-gallop gait transitions have been discussed in previous papers, no one article has tried to assimilate all the information. This review paper does this and includes a summary of the relatively new engineering (mathematical) approach to analyzing these transitions developed by Schoner et al. (29). The paper also presents unpublished data on gait transitions in cats and monkeys, and attempts to develop some general principles pertaining to trot-gallop transitions. Finally, the paper highlights areas where additional information is needed.