The strength model of self-regulation holds that self-regulation operates by consuming a limited energy resource, thereby producing a state called ego depletion in which volition is curtailed because of low energy. We present our research program on ego depletion as well as much relevant work contributed by others. Challenges to the theory have emphasized allocation rather than depletion of resources, research participant expectations and obligations, changes in motivation and attention, beliefs and implicit theories, perceptions about depletion and vicarious depletion, glucose anomalies, and feelings of autonomy. We conclude that the theory needs revision and updating to accommodate the new findings, and we indicate the requisite changes. Furthermore, we conclude that the strength model is much better able than the rival accounts to explain all available evidence. Most of the rival accounts are compatible with it and indeed work best by sustaining the assumption that self-regulation relies on a limited resource.