Changes in pedagogy, technology, and resources have forced tremendous change in library instruction in the United States over the past few years. One educational factor has changed even more than learning theory or the technology we use to apply and explore it, and that factor is the characteristics of our user populations. Increasing diversity in students' age, ethnicity, and academic preparation, added to the increasingly interdisciplinary nature of academic curricula, makes it vital for us to question our assumptions about who and what we are teaching in libraries, and how we are teaching it. The "average"18- year-old college student prepared with basic research skills does not exist now, if indeed that average student ever did. Today's students have a wide spectrum of backgrounds and library experiences, ranging from novice to expert, from first-year to returning adult, from non-native English speaker to under-represented ethnic group. This paper discusses recent statistics, and experiences at Harvard University, Northeastern University, and the University of Washington libraries. (Contains 5 references.) (Author/AEF)