Histone deacetylase 6 (HDAC6) catalyses the removal of acetyl groups from the lysine residues of a series of non-histone proteins, e.g., α-tubulin, Hsp90 and cortactin. HDAC6 is a unique deacetylase enzyme that is related to various processes that may be important in oncological, immunological and neurological fields, which makes the study of selective inhibitors extremely important to understand the function of this enzyme and to validate HDAC6 as a drug target through the development of clinical candidates. Therefore, this review describes the structure-activity and structureselectivity relationships of HDAC6 inhibitors, which were divided into two main classes, bulky and lipophilic cap groups and inhibitors with phenyl linkers.