Recent articles on familiarity (e.g. Whittlesea, B.W.A., 1993. Journal of Experimental Psychology 19, 1235) have argued that the feeling of familiarity is produced by unconscious attribution of fluent processing to a source in the past. In this article, we refine that notion: We argue that it is not fluency per se, but rather fluent processing occurring under unexpected circumstances that produces the feeling. We demonstrate cases in which moderately fluent processing produces more familiarity than does highly fluent processing, at least when the former is surprising.