Throughout this chapter, we have introduced you to some of the leading theories in the field of personality research and have given you insights into how these theories can be applied in real-world situations. We have begun by examining personality in terms of the trait approach and covered trait models that included 16, 5, 6 and 3 factors. These models have had underpinnings in the language that people use to describe personality or with the neurobiological processes that ‘hard-wire’ people into reacting to situations in a habitual way. This chapter has also discussed the negative and positive sides to people’s personalities; we then noted how the trait approach could perhaps be too general and lack power to discriminate how people behave over a diversity of situations and contexts. We have also highlighted that people can sometimes behave in ways that differ from what the trait approach would suggest are their dominant traits, yet the trait approach is unable to account for this. We have looked at an alternative explanation for these phenomena by suggesting that human beings are inconsistent in their behaviour and that the situations that people find themselves in are the best predictors of their behaviour. Counter-arguments to this claim have led contemporary personality psychologists to adopt an interactionist approach, in which behaviour can be explained by a combination of situational and personality factors. In the last section, we have set out the ways in which psychologists have applied personality theories and research to a real-world setting, such as the field of health and illness.