The aim of these articles is to enhance understanding of, and to give insight into, the behavioral, emotional and adaptive difficulties of persons with mental handicap. The authors who are all clinical psychologists explain and explore the issue and phenomenon of challenging behaviors, the use of applied behavior analysis and behavioral intervention in these cases, as well as discussing the handling methods adopted by involved rehabilitation workers and family members. The case studies are written in Chinese only. Each case has been taken from real life, but the names and some related details are changed or omitted to preserve confidentiality. (Chinese version only)