This historical review notes that although the comparative approach is not new to social science research, it was not until the late 1960s and early 1970s that criminologists began exploring crime comparatively. Since these early efforts, there has been a slowly expanding body of criminological literature that uses comparative techniques. Similarly, comparative studies of justice systems have emerged relatively recently in the scientific literature. Following the historical review of comparative criminology and criminal justice, the article identifies the types of comparative research according to approach, scope, data, and design. The benefits of comparative research are then identified, followed by a review of the sources of comparative data and the validity of the findings based upon those data. A section on types of comparative data addresses official data, survey data, and individual data-collection activities. A section on impediments to comparative research focuses on funding, access to research subjects, language differences, and finding an acceptable outlet in which to publish the findings. The article advises that these impediments to conducting comparative research must be addressed in order to maintain the momentum that has emerged over the last decade. In the short term, funding must be increased; and over the long term, academics must increase emphasis on comparative studies and the comparative perspective at their colleges and universities. In addition, scholarly associations in the fields of criminology and criminal justice must aid and mentor younger members in order to facilitate their successful entry into the comparative field. 10 notes and 72 references