This book is based on a one semester course for graduate students in physical sciences and applied mathemat- ics. Not detailed mathematical background is needed but the student should be familiar with the theory of analytic functions of a complex variable. Since the course is problem-solving rather than theorem proving, the main requirement is that the student should be willing to work out a large number of specific examples. The course is divided about equally into three parts, where the first part is mostly theoretical and the remaining two parts emphasize on problem solving.