Google Scholar, the beta Google service for searching scholarly information, crawls scholarly, web-based content--predominantly by targeting specific publishers with which Google has contractual arrangements. Open access material is crawled as well. These full-text materials, abstracts, and citations are being indexed, and citations from these papers to other sources are also extracted and indexed. So besides returned links to full-text articles, search results can also include citations to non scholarly materials and scholarly materials that Google has not crawled. This article discusses the challenges that Google Scholar faces.