Since Locke’s day, the mathematical theory of probability and statistics has greatly developed and has come to be used in almost every branch of science. Hand in hand with these mathematical developments have come developments in philosophical ideas about probability, so that there is now an intricate network of philosophical theories of probability. The aim in this book is to expound these theories and to explain how the various views are related to each other. – After some introductory material in Chapter 1 («Introductory survey of the interpretations : some historical background»), the next seven chapters give systematic expositions of the main philosophical interpretations of probability, which are presented in roughly the historical order in which they were developed. These are the classical (Chap. 2), logical (Chap. 3), subjective (Chap. 4), frequency (Chap. 5), propensity (Chap. 6 : I. general survey; and Chap. 7 : II, development of a particular version) and intersubjective views of probability (Chap. 8). Although some thinkers hold that there is only one correct interpretation of probability, and that the others are mistaken, such is not the view to be found in the present book : in Chap. 8, indeed, arguments are put forward for a pluralist conception of probability according to which there is more than one valid interpretation of probability, and different interpretations are suitable for different areas. This last thesis is illustrated in Chap. 9 («An example of pluralism : differences between the natural and social sciences»), where it is argued that probability has a different meaning in the natural sciences from its meaning in the social sciences. M.-M. V.