The article first reviews the three major sources of crime data: institutionalized systems such as the Uniform Crime Reports (UCR) and National Crime Survey, journalistic investigations and reporting, and scientific investigations. It emphasizes that all are highly interdependent because they rely on many of the same collecting systems. Because of variations in the kinds of crimes that are included in counts, units that are counted, and territory for which counts are made, the public is aware of only a relatively small amount of all kinds of crime. A major deficiency in crime reporting is the UCR's use of persons rather than households or organizations as its base. The paper then explores criteria that make a crime serious, with attention to legal punishments and sanctions, physical or economic harm, and psychic harm. The UCR underestimates both the seriousness of some events and the numbers of crimes by counting only the most serious of the offenses occurring in an event. The public appears to use different criteria from the police since they report more than two-thirds of all motor vehicle thefts and only one-half of all forcible rapes and robberies. Statistics show that the public also judges the relative seriousness of crime in terms of the value of property lost and the extent of personal injury. A summary of research on career criminals notes that they tend to be males living in large cities, are relatively young, and live near their victim, concentrating on a small number of residential areas. Furthermore, a substantial proportion of all offenders commit their crimes as members of offending groups. These findings suggest that group and juvenile offenses are more prevalent and more serious than the public and Government consider them to be. Finally, the article discusses crimes against property, such as vandalism and arson, which crime statistics gatherers often regard as less significant than crimes against persons. The article contains 217 footnotes. For related material, see NCJ 86552.