I have revised Moy-Thomas's widely used book on Palaeozoic fishes in an attempt to incorporate some of the considerable advances that have been made in this field over the last 30 years, which have in some respects made the first edition seriously out-of-date. The book is now inevitably longer, but its scope remains the same and the original approach has been main­ tained as far as possible. I have, however, undertaken a certain amount ofre­ arrangement of the contents, consonant with our changing views of fish evolution, and have tried to reflect some of the current preoccupations of students of fish evolution in expanded sections on mode of life and relation­ ships. The illustrations have been completely replaced, and in selecting the figures I have been faced with an embarrassing richness of source material. In an attempt to keep the figures down to a reasonable number, I have decided that it is better to have a few species illustrated with clear drawings than give thumb-nail sketches of all the forms mentioned in the text, and as far as possible to restrict the illustrations to Palaeozoic species. All the illustrations have been redrawn to a common style, and in some cases they have been specially prepared or modified for this book. Authors' names are now included in the text and a list of references is given at the end of each chapter.