In a world of more than seven billion people—who mostly reside in cities and towns—the Baltimore Ecosystem Study is recognized as a pioneer in modern urban social-ecological science. After two decades of research, education, and community engagement, there are insights to share, generalizations to examine, and research needs to highlight. This timely volume synthesizes the key findings, melds the perspectives of different disciplines, and celebrates the benefits of interacting with diverse communities and institutions in improving Baltimore’s ecology. These widely applicable insights from Baltimore contribute to our understanding the ecology of other cities, provide a comparison for the global process of urbanization, and inform establishment of urban ecological research elsewhere. Comprehensive, interdisciplinary, and highly original, it gives voice to the wide array of specialists who have contributed to this living urban laboratory.