The present paper summarizes experimental and clinical data indicating the therapeutic potential of the GABAB receptor agonist, baclofen, in the treatment of alcohol use disorder (AUD) and substance use disorder (SUD). Multiple preclinical studies have demonstrated the ability of baclofen to suppress alcohol drinking (including binge- and relapse-like drinking), oral alcohol self-administration, and intravenous self-administration of cocaine, nicotine, amphetamine, methamphetamine, morphine, and heroin in rodents. Some randomized, controlled trials (RCTs) and case reports support the efficacy of baclofen in suppressing alcohol consumption, craving for alcohol, and alcohol withdrawal symptomatology in alcohol-dependent patients. Data from RCTs and open studies investigating baclofen efficacy on SUD are currently less conclusive. Interest in testing high doses of baclofen in AUD and SUD treatment has recently emerged. Preclinical research has extended the anti-addictive properties of baclofen to positive allosteric modulators of the GABAB receptor (GABAB PAMs). In light of their more favourable side effect profile (compared to baclofen), GABAB PAMs may represent a major step forward in a GABAB receptor-based pharmacotherapy of AUD and SUD.