The Individual Assessment Profile (IAP), a structured intake assessment interview instrument in the public domain, was designed for use with substance-abusing populations in several large-scale and community-based drug abuse treatment projects underway in the United States. Background information is presented, including the content-based item-selection process used during the pretests and pilot testing. Validity and test-retest reliability data are also presented, along with descriptions of studies using the IAP for clinical, research, and management information purposes. Concordance between biological measures and self-reports of recent drug use, measures of internal consistency, and test-retest reliability coefficients were generally good. A computer-assisted personal interview version of the IAP and an automated reporting system were subsequently developed for clinical and management reporting purposes and used in a large-scale research demonstration project. An intreatment version of the IAP has also been developed to collect information on treatment services provided and to assess changes in behaviors after 3, 6, and 12 months of treatment. These instruments (the IAP intake and intreatment interviews) provide a comprehensive system to assess substance-abusing populations.