The process technologies for conversion of bio-feedstocks such as vegetable oils, animal fats, and algal oil into renewable diesel have been developed and commercialized during the last decade. The global annual production capacity of renewable diesel is approaching to 5.5 million tons per year. The refining process generally includes pretreatment of the renewable feedstock to remove impurities, hydroprocessing and isomerization to produce hydrocarbons, and distillation to produce a fuel suitable for use as diesel or jet fuel. This article reviews recent development in the commercial production of renewable diesel, pretreatment technologies, chemistry of deoxygenation and cracking of triglycerides, the effect of reaction parameters on the relative activities of different reaction pathways, catalyst development, and the technical details of commercial processes for refining bio-feedstocks.