Technical Abstract: Biodiesel is an alternative fuel made from vegetable oil or animal fat that can be employed in compression-ignition (diesel) engines. Biodiesel is more prone to start-up and operability problems during cold weather than conventional diesel fuels (petrodiesel). This work reviews impacts that exposure to low temperatures can have on biodiesel and its blends with petrodiesel. Pertinent fuel properties are defined and the relevance of their measurement accounted for in terms of assessing performance in the field. Impacts of small concentrations of monoacylglycerols, steryl glucosides and other minor constituents are discussed and methods to assess and reduce their effects are reviewed. Existing technologies for improving cold flow properties and performance of biodiesel are examined as follows: 1) adding commercial petrodiesel cold flow improver (CFI) additives; 2) developing CFI additives designed to improve properties of biodiesel; 3) transesterification of oil or fat with medium/branched-chain alcohols – either as an independent fuel or in admixtures with methyl (or ethyl) esters; and 4) fractionation by partial crystallization of dry melt or in organic solvent or by forming urea inclusion compounds. This work closes by providing an outlook for future studies on issues related to improving and maintaining biodiesel properties and performance during cold weather.