AbstractMajor difficulties for a novice physics problem solver are how to interpret new problems and how to combine information given in the problem with information already known. A domain expert, by contrast, has the knowledge to take full advantage of problem features at a glance. It takes a long period of practice to acquire such situational knowledge, and it would be desirable for this to be taught more effectively. As a first step, this requires information on how situational knowledge differs across individuals of different competence levels. Related research on mental models and problem representations does not give a direct view on the knowledge subjects have of situations before being confronted with the problem. To assess situational knowledge more directly, we asked participants to respond to physics formulas (from the field of electrodynamics) by describing relevant problem situations. We compared physics problem descriptions by experts (n = 6) and by proficient (n = 6) and less proficient (n = 6) novices. We analyzed the situations that were described at the levels of words, sentences, and complete descriptions. Results indicate that competence is related to the structure of problem situations rather than the use of particular concepts, and that the differences in the use of multiple representations are more prominent than differences in the use of one specific kind of representation. Results also indicate that the differences between experts and novices are along different dimensions than the differences between more and less proficient novices. Implications for teaching are discussed. © 2002 Wiley Periodicals, Inc. J Res Sci Teach 39: 928–951, 2002