As computers become an important part of everyday life, molecular modelling is affecting all parts of chemistry, and is particularly useful in organic chemistry. But how does it work? How reliable is it? What are its limitations? Is it useful for normal chemists? In answering these questions, this book aims to demystify molecular modelling, enabling the non-specialist to appreciate the power and the limitations of the computational tool available. The book provides a background to the methods used and describes how they have developed. It also shows how molecular modelling has been used to address chemical questions commonly asked by the experimental chemist, and includes many examples and case studies. It is aimed at undergraduates as well as researchers. A discussion are and enhanced images from the book are available online.