In two experiments, we examined how professional chemists (i.e., experts) and undergraduate chemistry students (i.e., novices) respond to a variety of chemistry representations (video segments, graphs, animations, and equations). In the first experiment, we provided subjects with a range of representations and asked them to group them together in any way that made sense to them. Both experts and novices created chemically meaningful groupings. Novices formed smaller groupings and more often used same-media representations. Experts used representations in multiple media to form larger groups. The reasons experts gave for their groupings were judged to be conceptual, while those of novices were judged to be based on surface features. In the second experiment, subjects were asked to transform a range of representations into specified alternative representations (e.g., given an equation and asked to draw a graph). Experts were better than novices in providing equivalent representations, particularly verbal descriptions for any given representation. We discuss the role that surface features of representations play in the understanding of chemistry, and we emphasize the importance of developing representational competence in chemistry students. We draw implications for the role that multiple representations—particularly linguistic ones—should play in chemistry curriculum, instruction, and assessment. © 1997 John Wiley & Sons, Inc. J Res Sci Teach 34: 949–968, 1997.