A major motivation for the development and ultimate replacement of petroleum-based fuels with alternatives is the desire to reduce the carbon emissions (i.e., CO2) created when burning hydrocarbon fuels in prime mover devices. In addition to CO2, combustion of hydrocarbon fuels in air will inevitably create a number of other emissions (e.g., NOx, soot, etc.), which can have detrimental effects on human health or the local (or global) environment. Furthermore, the desire for a more economic and stable fuel supply has also provided impetus for the identification of alternative feedstocks for fuels. With these motivations to find alternative fuels for power generation, it is important to understand how different fuels can impact pollutant formation. This chapter focuses on the fundamentals of pollutant formation in combustion, as well as the impact of various alternative fuels on the combustion generated emissions. This includes carbon monoxide, nitrogen oxides (NOx), and soot. These topics are addressed for a variety of candidate fuels, including hydrogen and ammonia.