The analysis of crime patterns clearly indicates that juveniles' involvement in homicide remains a serious problem in the United States in the 21st century. Homicide arrests of juveniles increased every year from 1984 through 1993. Although the number of minors arrested for murder declined between 1994 and 2000, the crisis is not over; the percentage of homicide arrests involving juveniles is still higher than it was in 1984. The research on juvenile murderers has been mostly descriptive. Psychogenic explanations (e.g., mental illness, defective intelligence, and childhood trauma) have predominated in the literature. Biopsychological explanations (e.g., neurological impairments and brain injuries) have also been investigated, as have data on key sociological variables (e.g., family constellation, gang involvement, drug and alcohol use, and peer associations). Sociological theories of criminal behavior, however, have not been systematically investigated. Some research has involved case studies of girls who have murdered. These studies show that girls are more likely than boys to kill family members and to use accomplices to do these murders. Research has also been devoted to homicides that have involved young children and case studies of adolescent murderers. Areas covered in these case studies include psychological disorders, neurological impairment, intelligence, home environments, involvement in other antisocial behavior, substance abuse, and other social deficiencies. In examining factors that contribute to the increase in juvenile homicide, the chapter notes that the existing literature on juvenile homicide rarely addresses the factors that fueled the recent dramatic increase in murders by juveniles that began in the mid-1980's. This chapter contains a section that supplements the existing literature on young murderers with a perspective that offers explanations for the shifts to more juveniles being involved in homicide in the United States, particularly from the mid-1980's to the early 1990's. After evaluating approximately 100 adolescents involved in murder, the author believes that many factors often act in concert when youths kill. These variables are grouped into five main categories: situational factors, societal influences, resource availability, personality characteristics, and their cumulative effects. 1 table and 240 references