This interdisciplinary Research Companion sheds light on territories located outside or far from urban centers. It discusses in detail the peripheralization occurring in these regions including low levels of social and economic progress, reduced infrastructure, migration outflow, and other challenges. Drawing on detailed case studies, the contributing authors assess contemporary socioeconomic, cultural and political structures; the root causes of spatial inequalities, including poor transport and the quantity of natural resources; and the threats that these marginal spaces pose to social cohesion. Expert contributors from a broad array of countries address diverse problems facing the periphery, such as depopulation and regional migration, inadequate rural funding, and marginalization. Ultimately, this Research Companion is a compendium of knowledge about the periphery that identifies, through a holistic approach, the key barriers in these regions. The Research Companion to the Periphery and Peripheral Regions is a vital resource for scholars and students of human and economic geography, as well as development and regional studies. Practitioners and planners will also benefit from its insights on spatial development and local and regional expansion strategies.