Functionalization of diamond surfaces holds considerable promise from both fundamental and applied research aspects. This review summarizes briefly the state of the art of chemical, photochemical and electrochemical strategies for the grafting of different organic functionalities on diamond. Depending on the sought-after application and the desired physical property of diamond, halogenated, aminated, carboxylated and oxidized diamond surfaces have been proposed. After a brief introduction, the review is primarily divided into two parts, presenting chemical functionalisation strategies used on oxygen-terminated diamond, followed by methods used for the formation of C–C, C–X and C–N bonds on hydrogen-terminated diamond.