Many books have been written about the pathology of the major organs of the body such as the lungs, heart, gastrointestinal tract etc. Included in these are descriptions - often with a minor emphasis - of pathological conditions which affect their serosal surfaces. In this book I have endeavoured to reverse the process and treat the mesothelium as an organ in its own right, rather than being the "no man's land" between various major structures. A number of pathological conditions are common to the coverings of the three major body cavities - the pleura, pericardium and peritoneum - while some abnormalities are exclusive to one or other sites. I hope that the contents of this book cover a broad enough spectrum of mesothelial diseases to be of help to service pathologists, who are ever increasingly being asked to make diagnoses, particularly on small biopsies of pleural and peritoneal tissues. It is also my hope that the various aspects of the subject have been dealt with in sufficient depth to be of use to pathol­ ogists engaged in teaching and research, and to those whose interests lie in the structure and function of the mesothelium. There is still much to be learned in understanding the way the mesothelium behaves in the realm of both inflammatory response and tumour formation. If this book provides a stimulus to furthering research in these fields I feel it will have achieved its objective.