The invention relates to crystalline forms of a β-nicotinamide mononucleotide (NMN), methods of their preparation, and related pharmaceutical preparations thereof. In one aspect, a crystalline compound of formula (I): In another aspect, a pharmaceutical composition comprising a crystalline compound of formula (I) and one or more pharmaceutically acceptable excipients. In yet another aspect, a method for preparing a crystalline compound of formula (I) comprising providing a mixture of a compound of formula (I) in a solvent and crystallising the compound of formula (I) from the mixture. The crystalline compound of formula (I) may be anhydrous or a solvate. Preferred solvents include dimethylsulfoxide, methanol and water. The solution may be brought to the point of supersaturation to precipitate out the compound of formula (I). This may be achieved by adding an anti-solvent or by cooling the solution to ambient temperature or lower.
