Waste biomass feedstocks (WBFSs) are considered major renewable reserves because of their limited life cycle, and WBFS-resulting biofuels are one of the possible alternatives to fossil fuels (FF). When WBFS develops, all carbon in WBFS comes from the atmosphere and is liberated into the environment when it is burned. Conversely, burning FF in engines releases greenhouse gas emissions (GHGs) that damage the environment. Bioenergy is generally considered one of the best substitutes for sustainable economic and industrial development. WBFS can be transformed into bioenergy through a range of routes, with emerging advances in the three major conversion pathways: biological, chemical, and thermochemical approaches. The most important and common biofuels for bioenergy comprise biochar, biobutanol, biodiesel, bioethanol, charcoal, liquefaction and pyrolysis biogas, synthesis gas (syngas), and bio-oils. This chapter details bioenergy, categories of bioenergy, numerous waste biomass feedstocks, bioenergy synthesis routes, circular bioeconomy, various pathways to boost bioeconomy, techno-economic outlook challenges, and future snags.