Many Web surfers maintain bookmark files containing URLs organized into folders which represent topics by function or content. We propose a new framework for discovering themes among such folders created by a community of surfers with overlapping interests. In principle, surfers need not create personal folders; they can just use a 'standard' tax- onomy such as Yahoo. In practice, a standard taxonomy is neither necessary nor sufficient; it is too detailed in most part, but likely to be inadequate in the community's areas of deep interest. Our framework, based on the minimum de- scription length principle, exploits two semantically different relations: "term occurs in document" and "document occurs in folder", and combines them without the need for heuris- tic weighting of attributes. Themes, in effect, finds common factors in people's interests when it can, while maintaining their individuality when it must. We present experimen- tal results to illustrate our framework and show how it is different from content-based clustering. We also propose a number of applications to finding themes, including collab- orative recommendation and resource discovery.