It is unlikely that anyone has had a greater impact on the methodology of scientific research in the twentieth century than Ronald Aylmer Fisher. From his early work in developing statistical methods needed for the interpretation of experimental data, he went on to recast the entire theoretical basis for mathematical statistics and to initiate the deliberate study and development of experimental design central to the whole process of the Natural Sciences. In clarifying the principles of inductive inference, Fisher greatly enlarged our understanding of the nature of uncertainty and contributed fundamentally to the philosophy of our age.This volume presents a selection from Fisher's letters on statistical inference and analysis and related topics. It also includes relevant material from the letters (from many distinguished scientists) to which he was replying. It is a companion volume to Natural selection, heredity, and eugenics: selected correspondence of R. A. Fisher with Leonard Darwin and others (ed. J. H. Bennett, Clarendon Press, Oxford, 1983).