This book was written at a time when the boundary integral and boundary element methods were at its infancy. At that time, theoretical and computational aspects were dispersed into different pieces in the absence of a unifying theme. The purpose of this book was to bring together classical and recent developments (circa 1992) in a way that is accessible to mathematicians, physical scientists, and engineers. Over thirty years since publication, the book still serves its originial purpose. Other similar books have appeared in the meanwhile.