This brief is part of a series describing population, health and environment issues in distinct geographic areas in the Philippines. Calabarzon is the second most densely populated region in the country, principally because it is the closest region to metro Manila. Because of its close proximity to Manila and the industrial and economic opportunities that exist there, Calabarzon is experiencing rapid urbanization. With the influx of people and rapid industrial growth, environmental issues such as pollution, solid waste management, conservation, and natural resource management will increasingly become major concerns. The report highlights four initiatives built upon principles of collaboration that are successfully addressing some of these concerns, including the Laguna Lake Development Authority, the Pollution Control Officers Initiative, a solid waste management project and the WWF Marine Conservation Project.