The Offenders Index (OI) is the standard research tool used for conviction studies. It is a database intended to contain all court disposals relating to standard list offenses since 1963 in England and Wales. The Police National Computer (PNC) is an operational policing database for the United Kingdom, which contains additional information on cautions, warnings, and dates of offense. It is not suitable for research into criminal histories. Police records from the period prior to its launch in 1995 are being computerized and integrated into the PNC database when more recent convictions are recorded. Records from the OI and the PNC data sources were matched at the individual and court date levels for offenders in five research studies. The matching process was carried out for over 18,000 individuals using purpose-written software. Records for 92 percent of these individuals were found in both the PNC and OI data and 91 percent of individuals were found to be matches or partial matches. Automatic matching of court dates by the purpose-written software was supplemented by manual intervention to match records with similar dates, using summary offense information, and to identify composite OI records. There were more than 178,000 court dates in the merged files with a 71 percent match, including 2 percent matched manually. The results of the matching process were used to propose an automatic matching algorithm to link court data level records with minimal intervention from the user. Results show that research and evaluation studies would be enhanced if the currently used OI was augmented with additional information from the operational PNC. 2 figures, 4 tables, 3 references