Research suggests that déjà vu is a fairly common experience, and that around 70% of the population have experienced it (Brown, 2003). People are sometimes unsure of whether or not they have had it, as it is such a subjective experience. Many people will have, at some point in their life, travelled to a new city or country and have a fleeting feeling that they have been there before, even though they know they have not. Such an experience is one example of the déjà vu experience. As you will see, psychologists tend to define it as a sensation of familiarity for something that you know to be unfamiliar. Most interestingly, it seems that the experience of déjà vu is, amongst other things, experienced more frequently when we are tired, stressed or intoxicated, experienced more by younger people, and is related positively to education and intelligence. (For a full account of factors associated with déjà vu experience, see Brown, 2004.) As such then, it is a topic that should resonate with psychologists of all ages and stages who are reading this book.