The chapter examines the growth and influence of cities throughout history. It discusses the roots of European urban expansion in medieval times linked to rise of merchant capitalism and colonialism. This helped spread the urban model globally. Today, most people live in urban areas and cities dominate aspects of modern life. The chapter analyzes urban systems, trends in core/peripheral regions, and rise of mega cities and world cities that occupy key roles in global economies and culture. Challenges include overurbanization, slums, and differences between core and peripheral urban areas.