Glycine betaine (betaine) acts as a methyl group donor in transmethylation reactions in organisms. Betaine occurs in numerous vertebrate tissues as an osmolyte, ensuring osmoprotection. Betaine is safe for piglets at the maximum supplementation rate of 2 000 mg/kg complete feed with a margin of safety below 5. This conclusion is extended to all pigs and extrapolated to all animal species and categories. The use of betaine anhydrous and betaine hydrochloride as feed additives up to a supplementation rate of 2 000 mg betaine/kg complete feed is unlikely to pose concerns for consumer safety. In the absence of data, betaine anhydrous and betaine hydrochloride should be considered hazardous by inhalation, as irritant to skin, eyes and mucous membranes, and skin sensitisers. The supplementation of feed with betaine anhydrous and betaine hydrochloride does not pose a risk to the environment. Betaine has the potential to become efficacious in all animal species and categories when administered via feed or water for drinking. Betaine anhydrous and betaine hydrochloride are considered as nutritionally equivalent sources of betaine. The FEEDAP Panel made some recommendations on (i) introduction of a maximum content for supplemental betaine in complete feed and water for drinking; (ii) avoidance of simultaneous use of betaine in feed and water for drinking; (iii) avoidance of simultaneous inclusion of betaine and choline chloride in premixtures; and (iv) protection of users when handling the additives.