The all-in-one mixer is an extremely compact, fully integrated aftertreatment system. It contains an annular metallic diesel oxidation catalyst (DOC), an AdBlue® / diesel exhaust fluid (DEF) mixer, an SCRoF, and SCR and a clean up catalyst (AMOX). The patented donut-swirl mixer efficiently decomposes and distributes the AdBlue / DEF exhaust gas mixture prior to the close-coupled SCR face. The annular design retains the exhaust gas heat to optimize SCR performance and minimize the potential of deposit formation. The downstream SCR substrates can be an SCR + SCR / CUC (cleanup catalyst) or an SCRoF (on filter) + SCR / CUC, depending upon the application requirements.