This monograph gives a coherent account of the theory of isolated singularities of complete intersections. One encounters such singularities often as the central fibers of analytic map-germs; that is why such map-germs (deformations) receive here a great deal of attention. The work treats both the topological side--including vanishing cycles and monodromy--and the analytic side--including properties of the discriminants of deformations_and explores the connections between them. It ends with a proof that the discriminant of the semi-universal deformation of an A-D-E singularity is isomorphic to the discriminant of the associated Coxeter group