This classic is one of the most cited and novel approaches to psychology ever written. Hans Eysenck presents a descriptive and causal model of human personality in accord with the major concepts of experimental psychology and the physiological and neurological mechanisms that form the biological basis of behavior patterns. His proposal for an alliance between personality and physiology represented a major innovation in the field of psychology, distinguished his research from his contemporaries, and set the stage for a wealth of research to come. Before this foundational work, Eysenck had initially constructed a model of personality in such works as Dimensions of Personality and The Experimental Study of Personality, but these were primarily descriptive in nature. A second phase of research included his Dynamics of Anxiety and Hysteria and Experiments with Drugs, where he provided causal analysis by reference to concepts then current in experimental psychology. The Biological Basis of Personality represents Eysenck's third phase, when he dug deeper to find biological causes underlying the psychological concepts of emotion, excitation, and inhibition--which had formed the building blocks of his earlier efforts. In this work, the causal links he postulates between personality variables and neurological and physiological discoveries establish a realistic model that takes theory out of the field of mere speculation. As Sybil Eysenck makes clear in her new preface, this book paved the way for a "marriage" of the experimental and individual difference approach in personality psychology. As Sybil Eysenck makes clear in her new preface, this book paved the way for a "marriage" of the experimental and individual difference approach in personality psychology.