Addiction is a chronically relapsing disorder characterized by compulsive drug use in spite of adverse consequences. Currently, there are very few effective treatments for addiction; in order to develop novel therapies, a clearer understanding of mechanisms underlying addiction is needed. Drugs of abuse induce lasting adaptations in corticostriatal and mesolimbic brain reward circuitry due to long-term alterations in gene expression. microRNAs, a class of non-coding RNAs, are powerful regulators of gene expression that bind to target mRNAs, thereby inhibiting their translation and/or causing degradation. miRNAs are increasingly implicated in gene expression changes underlying normal neuronal function as well as dysfunctions such as addiction and psychiatric disorders. This review summarizes plasticity- and drug-related miRNA expression patterns and functions in the context of corticostriatal circuitry, while proposing future directions that may reveal miRNA-mediated mechanisms regulating addiction-related behaviors in vivo. This article is part of a Special Issue entitled SI:Addiction circuits.