The relationship between human health and the environment is of great interest to researchers, policymakers, and the general public. Despite the realities of the situation, environment and health represents a rather nebulous construct: hard to see, hard to define, and hard to measure. Einstein defined the environment as everything that is not me; hence, impossible to measure. This article describes the evolution of the geographer's interest in the environment and health research; articulates the difficulties inherent in measuring the impacts of the environment on human health; and explores salient issues related to psychosocial health, environmental justice, and developing policy under scientific uncertainty.