The American Academy of Microbiology convened a colloquium February 6–8, 2004, in Portland, Oregon, to discuss environmental pathogens and the current state of research on these organisms. Scientists with expertise in infectious diseases, food microbiology, bacteriology, molecular biology, microbial ecology, pathogenic mycology, and other areas in the microbiological sciences participated. Participants considered the knowledge gaps related to the incidence and epidemiology of environmental infectious diseases, dynamics of human pathogens in our surroundings, ways to alleviate environmental infectious diseases, research needs in the field, and education and communication issues. Recommendations were made for how to proceed on these fronts. Environmental pathogens are defined as microorganisms that normally spend a substantial part of their lifecycle outside human hosts, but when introduced to humans cause disease with measurable frequency. They are borne in the water, soil, air, food, and other elements of our surroundings, and they affect almost every individual on the planet. Their adverse effects on human health and productivity cannot be controlled without first obtaining a thorough understanding of their environmental niches, their incidence, and the epidemiology of the diseases they cause. To achieve this understanding, surveillance of the environment to determine the numbers and distribution of environmental pathogens is needed, as is research into the microbial virulence and host factors that enable microbes to invade and damage human hosts. The key difference between environmental pathogens and other human pathogens is their ability to survive and thrive outside the host. Their widespread occurrence in the environment makes them difficult to monitor and control. Inroads have been made to understand the persistence of these organisms in the environment, the reservoirs they inhabit, the ways they exchange virulence factors, and their diversity, but a great deal more research is needed. By grouping together phylogenetically diverse organisms under the umbrella of “environmental pathogens,” it is hoped that the topic can gain the critical mass needed for sustained progress. Colloquium participants examined other research needs for the field, including the diagnostic and environmental technologies that will be necessary for taking the next steps. It was agreed that because of the complex nature of studying organisms that can exist in the environment and in human hosts, work in this area is best carried out in an interdisciplinary fashion with coordinated input from medical, molecular, and environmental microbiologists, specialists in host responses, epidemiologists, ecologists, environmental engineers, and public health experts. The development of improved diagnostic techniques is critical for accurate assessment of health risks and potential human or animal population impact associated with environmental pathogens. If the impacts of these diseases are to be effectively controlled, the techniques used to monitor and control infections by environmental pathogens—including interventions, exposure controls, drugs, and vaccines—require improvement. The processes surrounding drug and vaccine development must be tailored to the special problem of environmental pathogens, which often strike small numbers of individuals or individuals in less developed areas of the world and, therefore, offer less potential for drug development profit than more common diseases. A challenge exists, therefore, in meeting the need for targeted, specific interventions, including development of drugs and vaccines for infections by environmental agents, in the face of a lack of financial incentive for development of these tools. Finally, because the impacts of environmental pathogens can be felt by almost every person on the planet, the public needs to be better informed of their presence and risks. In too many cases, dissemination of information is relegated to the popular media. Professional societies can play an important role in educating the public as to the quantifiable risk posed by environmental pathogens and in encouraging critical interactions between scientists to move the field forward.