PAST ATTEMPTS TO DETERMINE THE ULTIMATE SOURCE OF U.S. CRIMINAL LAW HAVE FOCUSED ON A NUMBER OF THEORIES INCLUDING PLURALISM, CONFLICT, CONSENSUS, AND A BLENDING OF THESE EXPLANATIONS. CALIFORNIA LAW IS TAKEN AS A CASE HISTORY TO IDENTIFY THE FACTORS BEHIND CHANGES IN CRIMINAL CODES AND THE SOCIAL AND POLITICAL CLIMATE AT THE TIME OF EACH MAJOR CHANGE. DURING THE PERIOD 1955 TO 1971, CALIFORNIA LAW MOVED FROM A TRADITIONAL CODE WHICH HAD CHANGED LITTLE SINCE THE EARLY DAYS OF THE CENTURY TO A MORE PROGRESSIVE BODY OF LAW. DETAILS OF THESE CHANGES ARE GIVEN IN A SERIES OF CASE HISTORIES OF INDIVIDUAL BILLS. MOST OF THE MAJOR PENAL CODE REVISIONS DID NOT COME AT ONCE; INSTEAD A SERIES OF SMALL REVISIONS TO CLARIFY A POINT HERE OR THERE HAD THE ULTIMATE EFFECT OF BRINGING ABOUT MAJOR CHANGE IN THE LAW. LONGITUDINAL TRENDS ARE GIVEN FOR 12 DIFFERENT TYPES OF CRIMINAL JUSTICE ACTORS (DEFENDANTS, CONVICTED OFFENDERS, POLICE, PROSECUTORS THE JUDICIARY, AND CORRECTIONS OFFICIALS), FOR CRIMINALIZATION AND SEVERITY OF PENALTIES FOR CRIMES AGAINST PERSONS, CRIMES AGAINST PROPERTY, CRIMES AGAINST THE PUBLIC INTEREST, CRIMES WITHOUT VICTIMS, AND OVERALL CRIMINALIZATION. MULTIVARIANT ANALYSIS OF 700 SELECTED CODE CHANGES SHOWS THAT THE DETAILED CONTEXT OF THE CRIMINAL LAW HAS FAR MORE TO DO WITH EXERCISE OF POLITICAL POWER THAN WITH FUNDAMENTAL CONCEPTS OF WHAT IS MORALLY RIGHT. FORCES IN SOCIETY INFLUENCING THIS POLITICAL POWER ARE EXAMINED.