Previous research has identified areas under the foot where stimulation evokes specific tonic reflexes. The term "tonic" is used because these reflex movements occur slowly, as if tonus or tension were accumulating, in contrast to the abrupt phasic response of a tendon jerk. The concept of tonic reactions has now been incorporated into the design of dynamic foot orthoses to help provide improved orthotic treatment with a better functional outcome. This article describes the background of this technique, briefly describes the manufacture of the dynamic orthosis, and outlines some of its uses.