This book discusses the various principles in confocal scanning microscopy which has become a useful tool in many practical fields including biological studies and industrial inspection. The methodology presented in this book is unique and is based on the concept of the three-dimensional transfer functions which have been developed by the author and his colleagues over the last five years. With the 3-D transfer functions, resolving power in 3-D confocal imaging can be defined in a unified way, different optical arrangements can be compared and images of thick objects can be modelled with an insight into their inter-relationship, which makes the analysis easy. The aim of this book is to provide a systematic introduction to the concept of the 3-D transfer functions in various confocal microscopes, to describe the methods for the derivation of different 3-D transfer functions, and to explain the principles of 3-D confocal imaging in terms of these functions.