Abstract: The invention discloses creatine derivatives that are represented by Formula (I), Formula (II), and Formula (III); wherein Z is a functional group; Y is a mitochondrial targeting agent, a cationic ammonium group, or a polypeptide containing at least one positively charged amino acid residue; each R1 is independently hydrogen, alkyl, or a phosphate group; R2 a linker; R3 is a spacer group; R4 is hydrogen, alkyl, aryl, or heterocyclic; or R4 and R1, or R4 and R3, together with the nitrogen atoms to which they are attached form a heterocyclic ring, and W is hydrogen or alkyl.