The powerful influence of peers in human development has been widely documented, particularly within education. Throughout the history of higher education, peer interactions have been a component of scholarly explorations of student types, campus cultures, and even the cycle of student "generations." In addition, most student development theories attribute great significance to the process of maturation in interpersonal relationships and the impact of peers in this process. In addition to the influence of peers on personal development, higher education theory and research also show that they play a large role in student success and can affect students' transition to college, satisfaction, learning and academic performance, and persistence and retention. However, it is important to note that there is also evidence of negative peer influence, most notably with respect to relationships that focus on partying and socializing. Given the powerful and ubiquitous qualities of peer influence, higher education professionals have begun to harness this resource in student education, support, and service delivery by using undergraduate peers in leadership roles. This article serves as a foundation for the volume by providing a review of the literature on peer leadership. It identifies and discusses the many benefits of these programs to the students being served, to those who engage as peer leaders, and to the institutions themselves.