This paper illustrates ways in which concepts from fuzzy set theory may be applied to decision-making in the environmental sciences. Examples of its application to uncertainty, particularly in air pollution, are illustrated. No one of a number of methods for dealing with uncertainty is advocated, but rather a choice from a range of techniques should be made, appropriate to the application. Use of fuzzy sets formalises the underlying assumptions regarding uncertainty and therefore leads to better decision-making. This paper illustrates the flexibility of the approach, taking examples from air quality management, integrated pollution prevention and control, and human health assessment.