Mechanisms governing the fate of trace metals during coal combustion are reviewed, and new theoretical results interpreting existing data are presented. Emphasis is on predicting the size-segregated speciation of trace metals in pulverized coal-fired power plant effluents. This facet, which determines how trace metals originally in coal impact the environment, is controlled by fuel composition and combustion conditions. Multicomponent equilibrium calculations are used to predict vaporization/condensation temperatures for antimony, arsenic, beryllium, cadmium, chromium, lead, mercury, nickel, and selenium compounds in coal combustion flue gases, for a representative Illinois No. 6 coal. Experimental data show that equilibrium provides a good guide on the effect of chlorine on the partitioning of pure nickel, cadmium, and lead salts, introduced separately into a gaseous turbulent diffusion flame within an 82 kW combustor. Metal nuclei coagulation mechanisms are examined using existing computer codes, and these predict that coagulation does not allow condensed metal nuclei to be scavenged by existing coal ash particles. Rather, literature data on trace metal enrichment on small particles are consistent with processes of reactive scavenging of metals by larger particles, and it is suggested that these processes might be exploited further to convert these metals into environmentally benign forms.