The first of five volumes on the means by which Canadian communities can reduce the incidence of mental retardation, minimize existing impairment, and improve the quality of life of the mentally retarded, this booklet provides an overview of the types of conditions leading to mental handicap and what can be done to prevent or ameliorate those conditions. The approach is based on a four-level prevention model which distinguishes between impairment, disability, handicap, and the feedback role of the environment. After an introduction, there are sections dealing with the following specific topics and examples: known causes of mental handicap (fetal alcohol syndrome, child abuse); causes of handicapping circumstances (failure to diagnose mental handicap); the reality versus the label (a case study); recommendations for change (better antenatal and perinatal health records, frequent home visits to newborns); universal barriers to change (service delivery discontinuities); gaps and problems in Canada's existing system (need for better genetic counseling); causes for optimism--opportunities in Canada (better public understanding of mental handicaps); individual responsibility; and proof that changes can be made (the phenylketonuria story). (DB)