This work is based on the proceedings of a workshop on the Theory and Practice of Refinement held at the King"s Manor in York on 7th and 8th January 1988. The workshop covered industrial applications of refinement, case studies of new techniques, and the underlying theory. Although much of the material has a research orientation it should be readily understood by most formal methods practitioners. Thus the material should be of value to those wishing to apply refinement techniques in industry, as well as to researchers wishing to gain an understanding of current work in the area.