We tend to think of money as concrete and simple, a thing, but in fact it is multi-faceted and complex, more symbolic than actual. In the modern world it has come to take such a variety of forms that economists can no longer define it. On the other hand, our reliance on it causes us to invest it with a stability it does not and, probably, cannot have. Our ideas about money are, essentially, social defenses, and the money we think we have in our pockets or in our bank accounts is based on widely shared fantasies. The anxieties underlying these defenses spring from two sources: awareness that money's fixed values are unreliable, unable to protect us from loss, and an opposite irrational optimism about its capacity to grow magically. This paper suggests that the understanding psychoanalysis can offer about such common fantasies inextricably woven around money can provide the groundwork for an interdisciplinary collaboration with economics and the social sciences.