Thousands of minors are migrating unaccompanied to high-income countries. This special issue focuses on unaccompanied migrant minors from the Global South to Europe and the United States. In this introduction we seek to complement the contributions to this special issue by shedding light on what resources and experiences unaccompanied migrants arrive with, stressing these young migrants' challenges at each stage prior to arrival and the challenges they face navigating the receiving context. We first clarify how the international community defines "unaccompanied minors" or "unaccompanied children." We then provide brief histories of unaccompanied minors in immigration flows to the U.S. and the EU. Next, we review the literature on the experiences of unaccompanied minors before, during, and after migration. Finally, we discuss key themes and insights from the articles provided in this special issue.