Racial profiling of motorists by law enforcement officers involves using race as a key factor in an officer's deciding whether to make a traffic stop. This study found no comprehensive, nationwide source of information that could be used to determine whether race has been a key factor in motorist stops. The available research is currently limited to five quantitative analyses that contain methodological limitations; they have not provided conclusive empirical data from a social science perspective to determine the extent to which racial profiling may occur; however, the cumulative results of the analyses indicate that in relation to the populations to which they were compared, African-American motorists in particular, and minority motorists in general, were more likely than whites to be stopped on the roadways studied. Data on the relative proportion of minorities stopped on a roadway, however, is only part of the information needed from a social science perspective to assess the degree to which racial profiling may occur. A key limitation of the available analyses is that they did not fully examine whether various groups may have been at different levels of risk for being stopped because they differed in their rates and/or severity of committing traffic violations. Federal, State, and local agencies are in various stages of gathering data on motorist stops, and these efforts should augment the empirical data available from racial profiling studies. Eight appendixes provide supplementary data and information.