In this chapter, we will revisit some of the early biological theories discussed in Chapter 3 as we continue to explore why some people may commit crimes. We also take a turn from the sociological theories discussed in Chapter 4 and look at how scholars attribute criminal behavior to individual characteristics rather than one’s environment. Specifically, this chapter describes theories of intelligence, personality, psychological conditioning, as well as needs and motivations. The focus has gone from society to individuals with these theories.