Energy is the main basic need of today’s life. It is not only required in cell in the form of ATP but also required to spend life with ease and comfort in the form of fuels. Generally, fossil fuels like petrol, diesel, kerosene, and coal are the major energy sources in the current era. This source of energy progresses human being’s life like a boom in all aspects. But progress in these conventional fuels is destroying our own environment. It damages and pollutes the atmosphere air, water, and soil as well. These will risk our own life, and we will be destroying our planet. To overcome all these issues, alternative sources of “green energy” like bioethanol are the best option for damage control and to conserve earth. Microbes are tremendous players who produce bioethanol very efficiently using the fermentation process. Microbial ethanol, also known as bioethanol, will become one of the best options as an energy source. Bioethanol is safe and does not cause any harm to the environment. Currently, many countries are blending bioethanol with petrol and trying to completely replace it. Microbes have a very efficient fermentation ability to convert carbohydrate into ethanol. Microbial ethanol production is also cheap because microbes can use different lignocellulosic biomass agro-wastes (rice husk, sugarcane bagasse, rice straw, corn stock and corn cob, wheat straw, etc.) as feedstock; with this, it also controls the agro-waste pollution. This chapter emphasizes the different aspects of bioethanol production, different microbial sources, different production conditions, sources of substrates, and their economic feasibility.