Animal travel speeds have been hypothesized to satisfy several possible optimality criteria. These include (1) maximize net rate of energy gain (during foraging), (2) minimize energy cost per unit distance, and (3) minimize rate of energy expenditure. These criteria and others have, however, received little justification. General models of animal travel, coupled with the basic hypothesis that travel speeds are such that fitness is maximized, indicate that animals should sometimes behave in accordance with one of the above criteria. These models also indicate that animals should occasionally travel at their maximum sustainable speeds. In general, however, animals would be expected to travel at speeds that satisfy more complicated optimality criteria that include all the various counteracting factors.