Virtual organizations (VOs) - work organizations that rely fundamentally on the Internet rather than physical proximity for conducting their operations - promise to better leverage resources of all kinds throughout the world, and to improve the processes and the outcomes of collaborative knowledge work involving mutually remote partners. Their emergence as an increasingly standard paradigm for work has been meteoric, but has attracted relatively little empirical study. Much of the best empirical work on VOs has documented modest (or worse) success, and primarily focuses on describing risks and failure patterns. Our project complements this body of research by investigating what effectiveness means for virtual organizations, how VOs can achieve effectiveness, and how they can support knowledge work in new and distinctive ways. Given the growing importance of virtual organizations as a standard paradigm for knowledge work, it is vital better understand how they can be designed to be effective. One way to do this is to investigate how longstanding and successful virtual organizations function, and to try to refine that understanding into actionable design guidance for future virtual organizations.