Bio-aviation fuels are a major research and development topic, with strong interests from the aviation sector, the public, lawmakers and potential producers. Yet the development and market penetration in the air-transportation sector is slow, despite proven environmental benefits. Bio-fuels can indeed mitigate the environmental impact of the aviation sector mostly due to their low carbon intensity and favourable chemical structure. Such bio-aviation fuels must have "drop-in" characteristics with specifications and compatibility with the combustion behaviour of kerosene. The ASTM approval procedures are an important guarantee in this respect. Additional emission reductions rely on the production pathways, while optimum flight-related strategies are an additional benefit. An analysis of both the production pathways, and the environmental and Life Cycle Assessment findings delineates important research directions to enhance the production and use of bio-aviation fuels. Towards specific environmental issues, target research topics should include various topics. A better quantification of particulate and soot emissions, condensation contrails and NOx are of primary concern. The impact of geographic parameters on the bio-aviation fuel benefits should be investigated towards using bio-aviation fuels primarily in specific climate zones. Emission prediction models should be further developed. LCA approaches should be extended. More on-flight emission patterns should be measured to provide relevant data for the above considerations; Towards bio-aviation fuel characterization, safety and reliability are major criteria of the ASTM approval. Towards production pathways, the technical viability studies of synthesis pathways should be combined with economic assessments. Towards fuel costs, the reason for the high production cost of bio-aviation fuel is at least partly due to the oxygen-rich bio-polymer nature of biomass with unsuitable carbon chain length. In order to reduce the cost of bio-aviation fuel, several research directions are encouraged and discussed in the paper.