As the nature of work in today's organizations becomes more complex, dynamic, and global, there has been an increasing emphasis on far-flung, distributed, virtual teams as organizing units of work. Despite their growing prevalence, relatively little is known about this new form of work unit. The purpose of this paper is to present a theoretical framework to focus research toward understanding virtual teams and, in particular, to identify implications for effective leadership. Specifically, we focus on delineating the dimensions of a typology to characterize different types of virtual teams. First, we distinguish virtual teams from conventional teams to identify where current knowledge applies and new research needs to be developed. Second, we distinguish among different types of virtual teams, considering the critical role of task complexity in determining the underlying characteristics of virtual teams and leadership challenges the different types entail. Propositions addressing leadership implications for the effective management of virtual teams are proposed and discussed.