Modern obstetrics relies on a collection of drugs that affect the motility of the uterus either to stimulate or to suppress uterine contractions. Although a comprehensive, detailed understanding of how these drugs work does not yet exist, many, such as oxytocin, appear to work by altering cytosolic calcium levels in uterine smooth muscle cells. Other drugs, such as ritodrine, not only alter cytosolic calcium levels, but seem to inactivate myosin light chain kinase, a critical enzyme necessary for the initiation of uterine contractions. This report is intended to summarize the current state of knowledge regarding how these drugs affect the motility of the uterus. The delineation of the molecular mechanisms of action of these drugs is important because it provides the basis for their rational therapeutic use as well as for the design of new and better uterotrophic drugs.