The profession of town planning originated out of concerns for the health and well-being of people. Progress was made as crowded and unsanitary inner city slums were replaced with suburban environments where individuals could access green open spaces and clean air. With significant increases in urban populations and the geographic spread of the city, over time these environments became increasingly unhealthy. This paper provides an overview of how modern urban environments impact on people’s physical and psychological health. This understanding will assist planners and health professionals to ensure that HIA and other related impact assessment tools are effective in identifying and ameliorating potential adverse well-being outcomes of different urban policies and proposals for varying scales of development.