Folate (vitamin B9) is an essential water-soluble B vitamin critical for one-carbon transfer reactions in metabolism, including the biosynthesis of purines, pyrimidines, and methionine. It functions primarily as tetrahydrofolate (THF) derivatives that carry formyl, methyl, and methylene groups for DNA synthesis, repair, and methylation reactions. Naturally occurring in leafy vegetables, legumes, and fortified foods, folate prevents megaloblastic anemia and neural tube defects in pregnancy. The synthetic form, folic acid, is more stable and bioavailable. Deficiency causes elevated homocysteine and increased risk of cardiovascular and neurological issues. It is GRAS-approved for food fortification by regulatory bodies.