Ideally, the unit of analysis in psychology is the individual. However, many psychological methods do not cope well, either at the level of construct definition or at the level of measurement, with individuality in behavior. There is little leeway for constructs to be both idiosyncratically tailored to the individual, and still identified as having the same core meaning between individuals. Generally accepted ways to aggregate data in the course of empirically studying relationships simply ignore idiosyncrasy-but do so at some as yet undetermined costs. We identify, and illustrate with empirical data, the main features of an individually-oriented approach to general construct definition and measurement that seem to challenge the established concepts and norms of "good" measurement practice in behavioral research yet, at the same time, can be reconciled with them. (Contains 7 footnotes, 7 tables and 3 figures.)