This book represents an attempt to give the elements of modern statistics in a relatively rionmathematical form, but in somewhat more detail than is customary in texts designed for psychologists, and with considerably more emphasis on the theoretical rather than the applied aspects of the subject. It is designed as a text of at least an intermediate level of difficulty. I have felt for some time that the serious student in experimental psychology both needs and wishes to know somewhat more of the language and concepts of theoretical statistics than is provided in the usual "cookbook" of statistical methods.