Introduction What is a tip-of-the-tongue state (TOT)? People appear to know instinctively when they have TOTs, but as psychologists we nevertheless need a formal definition. A TOT is characterized by a delay in retrieving the word we are intending to say, a sense of imminence, sometimes called loosely feeling of knowing (FOK) the word, and a feeling of effort of active search for the target. What's more, in experimental settings where we induce TOTs using tasks such as responding to definitions, the word the person in the TOT state is searching for must be the target the experimenter has in mind. If this correspondence is verifiable - for example, by the participant eventually retrieving the word (resolution), the TOT is said to be objective. We might also accept a weaker criterion of objectivity if the participant recognizes that the experiment-supplied target was indeed the word for which they were searching. All other TOTs that are not verifiable in any way are called subjective. It is possible to take these three dimensions - delay, imminence, and effort - and use them to construct a three-dimensional lexical retrieval space (see Figure 6.1). Indeed, such a conceptualization is more generally useful because all types of normal and pathological disfluency fall within this space. Normal, near-instantaneous lexical retrieval lies at the origin. Aging, normal disfluencies, and pathological retrieval can all be described as vectors that shift retrieval from the origin to some other point in this space (see Figure 6.1). Effortful recall in the form of active search is a particularly interesting aspect of TOT, meaning that in TOTs, lexical retrieval is not as usual almost completely automatic, but instead involves what Harley, Jessiman, and MacAndrew (2011) call deliberative language processing - involving executive processing and placing a load on working memory (see Schwartz & Metcalfe, Chapter 2, this volume, for a discussion of similar issues from a metacognitive perspective).