For a legged system to operate on rough terrain, it must place its feet on footholds that provide good support and traction. This can be done by adjusting the step length, the distance traveled between successive steps. The author explores three methods for controlling step length: adjusting the duration of flight, the duration of stance, or the forward velocity. She has tested these three methods for step length control on a planar, two-legged machine in the laboratory. The strategies which adjust flight duration and forward velocity produce similar accuracy in following a pattern of footholds, but adjusting forward velocity allows a greater range of step lengths. Changes in stance duration are not large enough to produce a large change in step length. The author has used these methods to enable the biped to climb up and down a short flight of stairs.