The mesencephalic dopaminergic system plays a key role in the organization of goal-directed behavior, operating in three different domains: activation of the locomotor system via the dorsal corpus striatum, modulating motivational states and predicting rewards via the nucleus accumbens and amygdala, and planning strategies and monitoring errors via the prefrontal cortex. These operations are based on two modes of dopaminergic signaling. Tonic, longer-lasting dopamine release, and short-latency, phasic, stimulus-related dopamine release (70–100 ms poststimulus latency, less than 200-ms duration). Tonic and phasic release have been associated with distinct signaling systems provided by D1-like and D2-like receptors, respectively. The balance between these two signaling modes modulates the vigor, motivation, and flexibility of goal-directed behavior. I finally present a perspective that attempts to unify the multiple functions exerted by dopamine, in the context of evolutionary theory.