Computer simulation techniques have become almost essential in the study of the macro-molecular phenomena and phase behaviour on the molecular level. As these techniques become increasingly important, it is necessary to realize that they are useful tools, but are not the goals of research. With this distinction in mind, this work describes simulation techniques along with the physics behind the phenomena that these techniques simulate. Each chapter comprises three components - the general theoretical basis, an outline of the necessary computer code, and a few applications which illustrate the use of the technique demonstrated. The chapters also include examples of the typical practical problems that could be solved using each technique.