External fixation is now being used widely to maintain fractures, osteo- tomies, and arthrodeses in a desired position during consolidation. Whereas external fixation has been readily accepted in European countries, its use has weathered a rather stormy course in North America, especially in the treatment of fractures. Only recently has external fixation found its rightful place on this continent as well. Many different models are on the market today, and the practitioner is faced with a difficult decision in selecting a model. Should he buy a system where the fracture has to be reduced first, or should he work with a device permitting a reduction after insertion of the pins? To enable surgeons to study the different systems, to discuss their advantages and disadvantages, and to permit them to put their hands on these devices and inspect them personally, the Division of Orthopedic Surgery, University of Ottawa organized an applied basic science course in May 1981, External Fixation of Fractures. During this course, all major systems were pre- sented to the participants. As happened during the course "Internal Fixation of Fractures" held two years ago, the rigidity of internal fixation was frequently and intensively debated. Whereas the rigidity of internal fixation cannot be altered during the course of healing, the rigidity of external fixation can be changed. In fact, with progression of union, rods of increasing elasticity can be used.