A previewing system that permits selection from a plurality of interactive previewers for use in a system shell browser is disclosed. The previews may be extensible, such that different application developers may write custom previews for different file types, and the shell browser may follow established criteria to select an appropriate preview. The user may enter criteria to control which previewers are used for different situations, such as when certain file types are selected for previewing. Size of an available display area for the preview may be a criterion, such that resizing the preview area may cause a different preview to be displayed. The preview may be executed as a separate process from the browser so that crashes and hangs in the previewer process do not fatally affect the browser process. Previews may be incorporated within common file dialogs offered by an underlying operating system, such that different applications may share the common previewer.