A fundamental requirement of science is measurement. Without measurement there is no possibility of advancing understanding about the phenomena in question, beyond anecdotal and impressionistic accounts and testing and developing theories to build the discipline. In criminology and criminal justice a great deal of effort has been devoted to developing reliable measures of crime, as well as comprehensive measures of criminal justice processes and outcomes.

At the national level, there now exist three main sources of data about crime: (1) official crime reports based on police records; (2) crime victimization surveys; and (3) self-reports of criminal of ending. These data sources each have their strengths and limitations, which make them suitable for use in different contexts and for different purposes. Concerning the first of these sources, for many years some countries have published routine compilations of police records of crime, which are used as social indicators as well as to measure the workload of the criminal justice system. An excellent example is the Uniform Crime Reports (UCR), an assemblage of crimes reported to the thousands of independent law enforcement agencies in the United States. Because police records do not include the substantial numbers of crimes not reported by victims, some countries have more recently begun to conduct victimization surveys of sample of the general population. The best known of these surveys is the National Crime Victimization Survey (NCVS) conducted each year with thousands of households throughout the United States. Chapter 60 by Steven Block and Mike Maxifield describes both the UCR and NCVS. Until recently, self-report surveys of offending crime have mostly been used in research studies, but a national-level self-report survey, the Of ending Crime and Justice Survey, has now been initiated in the United Kingdom.