**Preface to "Optimization of Biodiesel and Biofuel Process"**

Although the utilization of green hydrogen as an energy vector for the decarbonization of the planet seems to be an irreversible decision, the transition from current energy sources to this new technology requires a period of no less than three or four decades. In addition, the enormous number of transport vehicles currently operating with diesel combustion engines must be considered because they must continue to operate throughout their useful life with diesel fuels or biofuels with similar properties.

To this very high number of vehicles currently in use, those that are currently being built and those with foreseeable construction in the next two or three decades must be added, providing that the deadlines set by the main car, truck, boat, and aircraft builders are met. Therefore, this energy transition needs the contribution of viable technical and economic solutions in order to gradually replace the fossil fuels currently used by several biofuels, both to reduce the levels of CO2 emissions and polluting emissions in cities that seriously affect the health of citizens.

In this Special Issue, a series of papers are collected that try to contribute to this effort, in order to enable the substitution of fossil fuels, in the greatest proportion possible in this transition period, which could be extended even for several decades. Thus, some research works are collected here that provide solutions to make the manufacture of conventional biodiesel more viable or that provide solutions for the reuse of glycerin, which is currently being produced in conventional biodiesel production plants. With glycerin, which is practically a waste, it is proposed to manufacture additives that improve the quality of polluting emissions. Solutions are also provided to try to avoid the production of glycerin as a residue, integrating this molecule directly as a derivative in biofuels. However, the most viable and effective solution at this time would be the direct application of straight vegetable oils in triple mixtures, with fossil diesel and an organic solvent, of a renewable nature such as ethyl ether or ethyl acetate. Even non-renewable gasoline can be used in a triple blend to adapt the viscosity of vegetable oils for use in conventional diesel engines. These triple blends avoid any synthesis process for the production of a biofuel and are capable of making a current diesel engine work correctly, with high levels of substitution of fossil fuels and with a notable reduction in polluting emissions.
