The tip-of-the-tongue state (TOT) is the feeling that accompanies temporary inaccessibility of an item that a person is trying to retrieve. TOTs have been studied experimentally since the seminal work of Brown and McNeill (1966). TOTs are experiences that accompany some failed or slow retrievals, and they can result in changes in retrieval behavior itself, allowing us to study the interplay among experience, retrieval, and behavior. We often attribute the experience of the TOT to the unretrieved target, but TOTs are based on a variety of cues, heuristics, or sources of evidence, such as partial information, related information, and cue familiarity, that predict the likelihood of overcoming retrieval failure. We present a synthesis of the direct-access view, which accounts for retrieval failure, and the heuristic-metacognitive view, which accounts for the experience of the TOT. We offer several avenues for future research and applications of TOT theory and data.Keywords Tip-of-the-tongue states . Metamemory . Metacognition . Retrieval . Lexical retrieval As if waiting always for another word-"at the tip of the tongue" we say, one thinks of all the places tongues have been and what they learned there, names.-Robert Kelly (2009), "The Will of Achilles"The poet Robert Kelly expressed in this poem an experience most of us have shared-that is, the strong feeling that we know something that we cannot recall at the moment, usually referred to as a tip-of-the-tongue state. We define tip-of-thetongue states (henceforth, TOTs) as the conscious feeling that accompanies or reflects upon the cognitive process of retrieval when an item that a person is trying to retrieve is temporarily inaccessible. The TOT entails two components: a basic level-the cognitive level-which is the act of trying to retrieve from memory, and a higher level-the metacognitive level-which is the commentary or reflection upon the cognitive level (Bacon, Schwartz, Paire-Ficout, & Izaute, 2007). At the higher metacognitive level are conscious feelings: We are aware of this high-level reflection when we experience a TOT. At the lower cognitive level is the attempt to retrieve a missing item from memory. That is, TOTs have content: We feel we are about to be able to recall the item, although we cannot do so right now. Indeed, a TOT may be thought of as a premonition of possible retrieval success, rather than an experience of retrieval failure. Our focus will be on the TOT as a metacognitive experience.This two-part definition connects TOTs to fundamental issues in the study of human psychology-namely how experience, cognition, and behavior are related-dating back to the earliest concerns in psychology (Tulving, 1989; see Costall, 2006;Woodworth, 1931). Introspectionists were interested in the nature of consciousness, but foundered, not only on the replicability of their results, but also on the relation of these results to observable behavior (cf. Costall, 2006). TOTs are conscious experiences but, unlike those studied by the early introspectionis...