Fine-particle concentrations in the atmosphere and related human health impacts have been the subject of significant scientific research and regulatory development over the past couple of decades. Finer particles have been shown in epidemiological studies to be more strongly associated with adverse health outcomes than coarser particles, although the causal mechanisms responsible have not been definitively established. While the association between mortality and other health effects and particle mass show relatively consistent magnitudes of effects, there is considerably less agreement and consistency in the results from studies that have examined associations between health impacts and the composition of the fine particles. It has been known for more than 20 years that trace metals are enriched in the fine particles formed during coal combustion. Some of these metals are toxic at high concentrations, and reliable estimates of their emission rates in coal-fired plants are required to assist assessment of the relationships between fine-particle exposure and health impacts. In this paper, the current understanding of the health effects of fine particles, including the influence of compsition, and the factors that determine trace-element release and emission from full-scale plants, is reviewed.