This paper reports a study of the use of card sorts in the categorisation of fragments of object-oriented programs. We are interested in the way in which programmer’s think about code so that we might attempt to provide support for browsing and reuse within object-oriented environments. Hence, we have been exploring the use of knowledge acquisition techniques in order to elicit programmer’s knowledge about code. Our results showed that experts tended to focus upon the functional relationships between the code fragments, and that the novice group were much more concerned with objects and inheritance. We discuss these results in terms of claims that have been made about the naturalness of conceiving the world in terms of objects and their relationships.