The world at present is mainly dependent upon petroleum-derived fuels for meeting its energy requirement. However, perturbation in crude prices, which concerns about long-term availability of these fuels coupled with environmental degradation due to their combustion, has put renewable alternative fuels on the forefront of policy maker's agenda. The diesel engines are considered workhorse in the global economy due to better thermal efficiency, ruggedness, and load carrying capacity. They, however, are also the main contributor to air pollution as they emit more oxides of nitrogen, suspended particulate matter as compared to gasoline engines. The most potential fuel either to supplement or to substitute diesel is biodiesel, butanol, producer gas, dimethyl ether, hydrogen, and so on. This chapter presents the developments about the use of alternative fuels in diesel engines. The exhaustive literature has evolved the main trends in the development of alternative fuels around the world. The chapter also describes the research directions on production and use of alternative fuels in off-road and transport vehicles powered by diesel engines.