Gas turbine engines for aircraft applications are complex machines requiring advanced technology drawing from the disciplines of fluid mechanics, heat transfer, combustion, materials science, mechanical design, and manufacturing engineering. In the very early days of gas turbines, the combustor module was frequently the most challenging. Although the capability of the industry to design combustors has greatly improved, challenges still remain in the design of the combustor, and further innovations are required to reduce carbon emissions. Many companies in the aviation industry committed to a pathway to carbon-neutral growth and aspire to carbon-free future in 2008. Additionally, airframers have aggressive goals to reduce carbon dioxide emissions by 50% by 2050 compared to those in 2005. Achieving these goals require technology advancements in all aspects of the aviation industry including airframers, engine manufactures fuel providers, and all the associated supply chains. The focus of this chapter is the influence of one module of the aircraft engine – the combustor.