Since global climate and health issues are becoming more urgent, many countries have made pledges towards carbon reduction and net zero within the next decades. Defossilization is one major aspect in such scenarios. The increasing introduction of renewable power goes along with a different focus and new opportunities for combustion science and applications. Alternative fuels and fuel blends as well as novel combustion and aftertreatment strategies aim to reduce the carbon footprint and local emissions. From a chemical viewpoint, such measures introduce exciting research questions regarding in-depth information on the combustion process, including detailed, fundamentally founded reaction mechanisms and physico-chemical combustion models of predictive character. Progress relies increasingly on valuable combinations of experiments, theory, simulation, and data strategies. The talk will highlight some recent examples of combustion chemistry research within this general discussion. Powerful in-situ diagnostic methods are applied to probe reactive systems in laboratory configurations. Results from prototypical fuels will be shown also to provide some guidance for further theoretical studies and model development. Such selected examples can serve as food for thought about chances and challenges in the transition towards carbon-reduced processes.