The Youth Leadership Institute (YLI), was founded in 1989 to address the clear need among youth-serving institutions, such as schools and school districts, community organizations, health care providers and the public health system, and the juvenile justice system, to give young people a real say in the key decisions, programs, and systems that affect them. Spanning more than fifteen years, YLI's experience in promoting youth leadership has revealed the importance of working on two fronts to engage youth in creating better systems and communities. YLI works with groups and decision makers "inside" systems and institutions (that is, schools and government) to educate, inform, and partner with them to map and build an infrastructure that supports inclusive youth participation and leadership and create tools for them to make the process work. YLI also works with "outside" groups (that is, community coalitions and organizers) to advocate for change on the part of youth-serving systems and communities. The underlying principle of this article is that some of the mystery around the meaning of youth leadership development, and around what youth "leadership" means for youth "development", can be solved by accounting for the potential connections, as well as the potential tensions and conflicts, between the Inside and Outside approaches. The authors begin by presenting a brief look back at the nation's legacy of youth civic engagement and a review of the research literature on youth leadership, as a means of setting the context for how youth leadership has traditionally been conceived and to suggest some of the links between the leadership demonstrated in both Inside and Outside efforts. Next, they look at YLI's own experience with three program pathways that support both Inside and Outside strategies, as a means of showing in practice how the two approaches diverge. They then discuss ways in which Inside and Outside approaches to youth leadership need to be cultivated at the levels of individual skills, collective processes, and youth-adult partnerships, and also how lessons from Outside approaches can help imbue Inside approaches with a greater emphasis on action and social justice. The article concludes with some thoughts on future research needs on youth leadership through an Inside-Outside lens, and with a challenge to practitioners and policymakers. (Contains 7 notes.)