The current chapter examines some of the salient psychological approaches to leadership. These approaches attempt to explain the emergence and effectiveness of leaders in terms of psychological variables, notably individual differences in the capacity to influence others. Psychology has provided valuable information to explain why certain individuals are more likely to become successful leaders than others. Indeed, leadership has been studied in psychology for over a century and the past twenty-five years or so have seen an exponential increase in the number of peer-reviewed research articles on the subject. This pattern (shown in Figure 9.1) is by and large a consequence of the revival of the person or trait approach to leadership (discussed in Sections 9.2 and 9.5), which emphasises the personal attributes (e.g., personality, charisma, intelligence and creativity) that explain interindividual differences in leadership. Importantly, the validation of the trait approach to leadership has key implications for assessment and personnel selection as it provides a conceptual and methodological framework for predicting future leadership at work and for hiring applicants with the greatest leadership potential; hence a great deal of this chapter is dedicated to the trait approaches to leadership.