The effects of stress on learning and memory are not always clear: both facilitating and impairing influences are described in the literature. Here we propose a unifying theory, which states that stress will only facilitate learning and memory processes: (i) when stress is experienced in the context and around the time of the event that needs to be remembered, and (ii) when the hormones and transmitters released in response to stress exert their actions on the same circuits as those activated by the situation, that is, when convergence in time and space takes place. The mechanism of action of stress hormones, particularly corticosteroids, can explain how stress within the context of a learning experience induces focused attention and improves memory of relevant information.