Object oriented programming is a way of thinking about problems. Smalltalk is one of the purest incarnations of an object-oriented programming language. Using a pedagogical approach, this book covers all aspects of object oriented programming: first through the study of various preexisting Smalltalk classes, their implementation and use; then through a detailed description of an implementation of an interactive Lindenmayer system and through implementation of a series of calculators. The author addresses such subjects as graphics programming, dependency mechanisms and hierarchical specialization. This book fills the gap for an in-depth self-study reference, permitting the reader to master all aspects of object-oriented programming through a large set of exercises with highly detailed resources.