This chapter reviews the microbial production of 2-keto-L-gulonate (2-KLG). Biotechnology-based alternatives to the Reichstein process have focused on the biological production of 2-KLG, one of the last intermediates of the Reichstein process. The conversion of 2-KLG to ascorbate (ASC) entails first an esterification to 2-KLG methyl ester, formation of a metal ascorbate salt and lactonization with acid into ASC. The one-step heterotrophic production of ASC by fermentation requires, among other things, a microbe that makes the L-isomer of ASC. The development of such a process has been hindered by ASC's oxygen lability, resulting in degradation of any ASC made and excreted by cells in an aerobic fermentor. Virtually all microalgae are fundamentally photosynthetic organisms, although some microalgae such as Poteriochomonas and Euglena have modest heterotrophic capabilities and some microalgae, such as Chlorella, have robust heterotrophic capabilities. New methods for the industrial-scale production of ASC are now challenging the traditional Reichstein process.