This project discusses university physics students’ use of models when explaining phenomena involving interaction between matter and electromagnetic radiation. This is a content area which is heavily modelled and appropriate explanations for the chosen phenomena draw upon a number of different models. University physics students are familiar with the phenomena, but they are not generally used as exemplars of scientific models within undergraduate physics education. The data for this study, which is collected during the beginning of 1999, comes from written surveys and interviews. The sample is third year university physics students at different universities in UK and Sweden. Both surveys and interviews have been through a piloting phase.