Amid rising environmental concerns, the aviation sector is under mounting pressure to decarbonize and transition toward more sustainable fuel alternatives. The limited availability of fossil-based jet fuels, coupled with global emissions targets, underscores the urgent need for a renewable aviation fuel solution. This chapter provides a comprehensive overview of bio-aviation fuelBio-aviation fuel development, highlighting its classification, feedstock options, and production technologies from a circular economyCircular economy perspective. It examines first- to fourth-generation biofuel sources including edible oils, non-edible oilsNon-edible oils, algaeAlgae, and genetically modified organisms, while emphasizing their availability, economic viability, and environmental impact. The core emphasis is placed on the Hydroprocessed Esters and Fatty AcidsHydroprocessed Esters and Fatty Acids (HEFA) (HEFA) pathway, which is currently the most commercially mature method for producing synthetic paraffinic kerosene (SPK). The chapter further outlines the essential process steps in HEFA fuel production, including deoxygenation, isomerizationIsomerization, and cracking. By integrating waste utilization and low-carbon processes, HEFA-based bio-aviation fuelBio-aviation fuel offers a promising route to achieving both environmental sustainabilityEnvironmental sustainability and aviation fuel security.