The scientific investigation of water-in-fuel emulsions spans over five decades; however, the widespread implementation of emulsion fuels in commercial settings has proven to be a challenging endeavor. This Perspective discusses the current status of the research pertaining to the formation and stability of emulsion fuels, technical and regulatory challenges, and opportunities. In particular, we highlight the need for a coordinated effort between the colloid and interface community and those actively investigating emissions, spray characteristics, and combustion aspects in internal combustion engines.