This report is the summary of the fourth workshop of The Roundtable on Environmental Health Sciences, Research, and Medicine. Environmental Indicators: Bridging the Chasm Between Public Health and the Environment, continues the overarching themes of previous workshops on rebuilding the unity of health and the environment. The purpose of the workshop was to bring people together from many fields, including federal, state, local, and private partners in environmental health, to examine potential leading indicators of environmental health, to discuss the proposed national health tracking effort, to look into monitoring systems of other nations, and to foster a dialogue on the steps for establishing a nationwide environmental health monitoring system. This workshop brought together a number of experts who presented, discussed, and debated the issues surrounding the implementation of a monitoring system.