Despite the influence of leadership in our lives, it remains poorly understood by most of us. This review defines leadership as "a combination of position, responsibilities, attitude, skills, and behaviors that allows someone to bring out the best in others, and the best in their organization, in a sustainable manner." There are many traits and skills demonstrated by leaders. These include talent, drive, willpower, practical wisdom, loyalty, ethical behavior, emotional intelligence, integrity, self-awareness, and resilience. However, to best understand leadership we focus on what leaders are actually required to do, rather than on the skills and traits used to accomplish these tasks. We review nine functions that are at the core of leadership: serve as the public face of the organization; articulate the vision and mission; create culture; strategic planning; decide what to focus on; select, and develop, the right people; establish a decision-making process; manage your boss; and be responsible 24/7. All leaders operate in a specific context, during a unique point in the history of their organization, with a unique set of circumstances. What is required of the leader in one set of circumstances will change as those circumstances change. If the leader understands her core responsibilities, and if she develops the people, culture, and processes necessary to deal with a changing environment, she will have the self-awareness and support necessary to continue to lead successfully.