This thesis discusses information retrieval from multimedia archives. Multimedia archives are collections of documents containing a mixture of text, images, video and audio. This work focuses on documents containing visual material and investigates search and retrieval in collections of images and video, where video is defined as a sequence of still images. No assumptions are made with respect to the content of the documents: the collections are not restricted to a specific domain (e.g., images of fingerprints or collections of x-ray pictures). Instead we concentrate on retrieval from generic, heterogeneous multimedia collections. In this research area a user¿s query typically consists of one or more example images and the implicit request is: ¿Find images similar to this one.¿ In addition the query may contain a textual description of the information need. The research presented here addresses three issues within this area.