Chronic exposure to addictive drugs enhances cAMP response element binding protein (CREB)-regulated gene expression in nucleus accumbens (NAc), and these effects are thought to reduce the positive hedonic effects of passive cocaine administration. Here, we used viral-mediated gene transfer to produce short- and long-term regulation ofCREBactivity inNAcshell of rats engaging in volitional cocaine self administration. Increasing CREB expression in NAc shell markedly enhanced cocaine reinforcement of self-administration behavior, as indicated by leftward (long-term) and upward (short-term) shifts in fixed ratio dose-response curves.CREBalso increased the effort exerted by rats to obtain cocaine on more demanding progressive ratio schedules, an effect highly correlated with viral-induced modulation of BDNF protein in the NAc shell. CREB enhanced cocaine reinforcement when expressed either throughout acquisition of self-administration or when expression was limited to postacquisition tests, indicating a direct effect of CREB independent of reinforcement-related learning. Downregulating endogenous CREB in NAc shell by expressing a short hairpin RNA reduced cocaine reinforcement in similar tests, while overexpression of a dominant negative CREB S133A mutant had no significant effect on cocaine self-administration. Finally, increasing CREB expression after withdrawal from selfadministration enhanced cocaine-primed relapse, while reducing CREB levels facilitated extinction of cocaine seeking, but neither altered relapseinducedbycocaine cues or footshock stress. Together, these findings indicate thatCREBactivity inNAcshell increases the motivation for cocaine during active self-administration or after withdrawal from cocaine. Our results also highlight that volitional and passive drug administration can lead to substantially different behavioral outcomes.