The idea of arousal as a non-specific state of activation has been implicated as an explanatory factor for many aspects of human behavior, ranging from emotional experiences to learning and memory. Critiques of this concept have highlighted that arousal is ambiguous and evidence for its role in emotion is mixed. However, contemporary emotion theories and empirical research continue to incorporate the concept of arousal in ways that fail to address its problems. Here, we review the origins of the term arousal in physiology and trace how it has been translated and applied to psychology (particularly as it relates to emotion). We consider whether the construct of arousal is currently (a) consistent and (b) useful in understanding human behavior.