The purpose of this chapter is to create a framework of homicide that will help the reader have a better understanding of the homicide process and about those who kill. Besides addressing some of the social issues and theories of homicide, it will take the reader through the historical aspects, beginning with the 1960s as a lead-in to understanding homicides in the past and where we are today. Since most cold cases occurred during these decades, this information should be enlightening. The chapter will discuss some of the research regarding solvability of homicides and will end with a full discussion of the four phases of homicide. All of this will go a long way toward helping the reader understand the challenges faced by the detectives charged with investigating and solving these cases, “hot” or “cold.”