Attention and memory cannot operate without each other. In this review, we discuss two lines of recent evidence that support this interdependence. First, memory has a limited capacity, and thus attention determines what will be encoded. Division of attention during encoding prevents the formation of conscious memories, although the role of attention in formation of unconscious memories is more complex. Such memories can be encoded even when there is another concurrent task, but the stimuli that are to be encoded must be selected from among other competing stimuli. Second, memory from past experience guides what should be attended. Brain areas that are important for memory, such as the hippocampus and medial temporal lobe structures, are recruited in attention tasks, and memory directly affects frontal-parietal networks involved in spatial orienting. Thus, exploring the interactions between attention and memory can provide new insights into these fundamental topics of cognitive neuroscience.