The theory of exterior differential systems provides a framework for
systematically addressing the typically non-linear, and frequently
overdetermined, partial differential equations that arise in
differential geometry. Adaptation of the techniques of microlocalization
to differential systems have led to recent activity on the foundations
of the theory; in particular, the fundamental role of the characteristic
variety in geometric problems is now clearly established. In this book
the general theory is explained in a relatively quick and concrete
manner, and then this general theory is applied to the recent
developments in the classical problem of isometric embeddings of
Riemannian manifolds.