R A Fisher's classic The Genetical Theory of Natural Selection was first published by the Oxford University Press in 1930. It was the first attempt to assess and explain Darwin's evolutionary theories in terms of the genetic processes underlying them, and was also original in being the first book to establish a firm theoretical basis for evolution. Since then, it has become a classic text in evolutionary biology, with Fisher hailed as one of the greatest evolutionary biologists of this century. This Variorum edition will be the definitive version - the only version of The Genetical Theory in print: it will include both Fisher's original 1930 text and that of a second edition of the book, published by Dover publications in 1958, which is now out of print. It also has a new Foreword, some unpublished material by Fisher that he wrote in his own copy, and letters between Fisher and Darwin's grandson, Leonard Darwin. Students, researchers, and general readers with an interest in the history of evolutionary biology will welcome this new edition.