Many proteins have been implicated in synaptic and experience-dependent plasticity. However, few demonstrate the exquisite regulation of expression and breadth of functional importance as the immediate early gene product Arc. Here we review and attempt to synthesize the disparate views of Arc in neuronal function. The main conclusion garnered from this body of work is that Arc is a critical effector molecule downstream of many molecular signaling pathways and that dysregulation of Arc expression can have dire consequences for normal brain function.