Abstract: Provided are certain histone deacetylase (HDAC) inhibitors of Formula I, or pharmaceutically acceptable salts thereof, compositions thereof, and methods of their use. The condition or disorder mediated by HDAC comprises a neurodegenerative pathology. Accordingly, also provided is a method of treating a neurodegenerative pathology mediated by HDAC in a subject in need of such a treatment, comprising administering to the subject a therapeutically effective amount of at least one compound, or pharmaceutically acceptable salt thereof, described herein.