The increasing availability of digital images, video, and audio has created exciting new research challenges on the organization of multimedia data for a variety of purposes. While some of these challenges relate to computational techniques (e.g., automatic extraction of visual features for automatic indexing of visual data), others are conceptual in nature (e.g., design of templates for manual indexing of visual data). The key issues are what to index from the data, how to perform the indexing of the data, and how to organize the indices obtained. The indices used to describe content as well as the organization of those indices have a tremendous impact on applications, particularly on large digital libraries where different types of media need to be stored and accessed. Relevant efforts in this direction include the emerging MPEG-7 standard [5], which aims at standardizing tools for describing multimedia data.