This book provides a comprehensive, detailed and self-contained account of four dimensional simple supersymmetry and supergravity. It will be an indispensable source of reference for advanced graduate students, postdoctoral and faculty researchers alike working in quantum field theory, high energy physics, gravity theory, mathematical physics and applied mathematics. The authors develop the subject in its superfield formulation but where appropriate for illustration, analogy and comparison with conventional field theory, they use the component formulation. Throughout the book the authors develop their material in detail with calculation and full discussions of the fundamental ideas and motivations. They discuss many subjects which until now could only be found in the research literature. In addition they present a plethora of new results. The result is the most comprehensive book yet produced on the fundamentals of supersymmetry and supergravity. After studying this book readers should be well prepared to pursue independent research in any area of supersymmetry and supergravity.