Novel cysteine prodrugs and their use in the treatment of diseases and/or conditions, including but not limited to diseases and/or conditions of the Central Nervous System (CNS), including but not limited to schizophrenia, drug craving, drug addiction, bipolar disorder, anxiety, depression, Parkinsons disease, Alzheimers disease, cognitive dysfunction, multiple sclerosis, Amyotrophic lateral sclerosis (ALS), ischemic stroke, HIV dementia, and Huntingtons disease.