Real world phenomena are permanently changing with various speeds of change. Repeating of four seasons in a year accompanied by appropriate changes in nature, alternation of day and night within twenty four hours, heart pulsations, air vibra­ tions that produce sound or stock-market fluctuations are only several examples. Furthermore, since most of these problems express nonlinear effects characterized by fast and short changes, small waves or wavelets are an ideal modeling tool. An oscillatory property and multiresolution nature of wavelets recommends them for use both in signal processing and in solving complex mathematical models of real world phenomena. As a professor at the School of Mathematics, who teaches computer science students, I feel the need to bridge' the gap between the theoretical and practical aspects of wavelets. On the one side, mathematicians need help to implement wavelet theory in solving practical problems. On the other side, engineers and other practitioners need help in understanding how wavelets work in order to be able to create new or modify the existing wavelets according to their needs. This book tries to satisfy both wavelet user groups; to present and explain the mathematical bases of the wavelet theory and to link them with some of the a-eas where this theory is already being successfully applied. It is self contained and no previous knowledge is assumed. The introductory chapter gives a short overview of the development of the wavelet concept from its origins at the beginning ofthe twentieth century until now.