Folate, also known as vitamin B9 or pteroylglutamic acid, is an essential water-soluble B vitamin critical for one-carbon metabolism, DNA synthesis, repair, and methylation reactions. It serves as a cofactor in the conversion of homocysteine to methionine and supports nucleotide biosynthesis. Naturally occurring in leafy greens, legumes, and citrus fruits, the synthetic form folic acid is used in fortification and supplements. Adequate intake prevents megaloblastic anemia and neural tube defects in pregnancy. Folate deficiency elevates homocysteine levels linked to cardiovascular risk. It is heat-labile and sensitive to oxidation, with bioavailability varying by food matrix and form.