This book is based on a course given at Massachusetts Institute of
Technology. It is intended to be a reasonably self-contained
introduction to stochastic analytic techniques that can be used in the
study of certain problems. The central theme is the theory of
diffusions. In order to emphasize the intuitive aspects of probabilistic
techniques, diffusion theory is presented as a natural generalization of
the flow generated by a vector field. Essential to the development of
this idea is the introduction of martingales and the formulation of
diffusion theory in terms of martingales. The book will make valuable
reading for advanced students in probability theory and analysis and
will be welcomed as a concise account of the subject by research workers
in these fields.