For most of U.S. history the vice president played little role in White House decision-making. In the 1970s this began to change. This dissertation uses a series of case studies of instances of vice presidential influence (with a focus on national security issues) to identify how and why the vice presidency has became an important presidential advisor. Gathering information through interviews and existing literature, this dissertation examines several factors that have facilitated the rise of the vice presidency including: the expansion of presidential power and responsibility, the institutional growth of the vice presidency in terms of staff and access, and the modern trend of "outsider" presidents who take office with little experience in Washington DC or national security affairs. The dissertation concludes by examining the factors that allow vice presidents to potentially exercise influence and the presidential needs that make vice presidential influence more or less likely.