Vitamin B-6 is an essential cofactor that participates in a large number of biochemical reactions. Pyridoxal phosphate is biosynthesized de novo by two different pathways (the DXP dependent pathway and the R5P pathway) and can also be salvaged from the environment. It is one of the few cofactors whose catabolic pathway has been comprehensively characterized. It is also known to function as a singlet oxygen scavenger and has protective effects against oxidative stress in fungi. Enzymes utilizing vitamin B-6 are important targets for therapeutic agents. This review provides a concise overview of the mechanistic enzymology of vitamin B-6 biosynthesis and catabolism. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology. (C) 2011 Published by Elsevier B.V.