Co-processing of different biomass with coal, plastics, vacuum residue, and vacuum gas oil can be very good sources of generation of transportation fuels with value-added chemicals, high heating value chars. Biomass has been converted to fuels, and value-added chemicals using, liquefaction, solvent extraction, gasification, pyrolysis, fast pyrolysis, steam pyrolysis, Fischer Tropsch process, fermentation to bioethanol, hydrodeoxygenation, transesterification and combustion. But their availability as a feedstock is very limited. Thus, co-processing comes as a versatile technology. The effect of the various experimental parameters such as temperature, type of feed, the blending ratio, type of reactor, catalyst type on the conversion yields and yield type has been discussed. Co-processing of biomass with coal, vacuum residue, plastics, and waste oil has also been discussed to give an in-depth detail of the research in this area. The co-processing indicates a series of reactions taking place between the reactive moieties of biomass with that of the other fuel sources leading to the formation of gasoline as well as diesel range hydrocarbons in the liquid product obtained. The synergism of the co-processing reactions is also established. Thus, co-processing can pave a path for generation of the most sought after fuels incorporating the bio-oils and seed oils into the existing refinery and creation of bio-refinery. This would bring about a leading step toward a bio-economy with lesser environmental impacts.