The review of causation theories for drug and alcohol addiction encompasses disease theories, gateway theories (progress from soft to ever harder drug use), social theories, psychological theories, psychosocial theories, lifestyle theories, and chemical-as-causative-factor theories. The theories most often used by clinicians are the disease, social, and psychological models. The most practical approach favors incorporating the best contributions from each theory. The purpose of the assessment model of the Brazos County Adult Probation Department is to obtain and synthesize information on probationers in order to make treatment decisions. Assessment focuses on determining the probationer's degree of involvement with specific drugs and alcohol; distinguishing between use, abuse, and dependence; and making treatment and followup recommendations. Components of the model are case histories, interviews, testing, education, and evaluations. The assessment process is sequential, providing an opportunity to gain increased understanding of the probationer's substance abuse habits as additional information is collected. The process consists of identification and referral, screening evaluations, diagnostic evaluations, and treatment recommendations. The process involves constant interaction between therapists and probation officers to ensure continuity of care. 31-item bibliography.