Effective leadership is widely considered a critical ingredient of team success, and some scholars have argued that abdication of leadership in any team is a recipe for failure (Sinclair, 1992; Zacarro, Rittman, & Marks, 2001). However, much of the existing research on team leadership has focused exclusively on external leaders serving in a formal capacity in the organization (Kozlowski & Bell, 2002; Stewart & Manz, 1995), while largely ignoring the processes and impact of internal team leadership. This dissertation addresses this shortcoming in our understanding of team functioning and team leadership by studying internal team leadership roles, which are often informal and emergent.

I extended previous work on external team leadership roles in order to articulate a comprehensive yet parsimonious set of four team leadership roles - Navigator, Engineer, Social Integrator, and Liaison - that may be engaged in by members of teams, not just formal leaders. I examined how time and team-level role differentiation serve as moderators of the relationship between these four leadership roles and individual contributions to the team. I also articulated three individual-level role-structuring processes - role overlap, role switching, and role sharing - and examined the benefits and challenges of these three individual processes across time by looking at their relationship with team member outcomes such as individual contributions, satisfaction with the team experience, and role stress - namely role conflict and role ambiguity (Jackson & Schuler, 1985; Tubre & Collins, 2000).

I tested hypotheses for this dissertation using data from 24 consulting teams in a multilevel longitudinal design. Data were collected primarily through surveys administered to team members at three points in time (beginning, middle, and end of projects). The primary statistical techniques were regression and hierarchical linear modeling. Findings showed support for the validity of the four leadership roles, as well as their ability to predict individual contributions to the team. The findings also demonstrated that both time and role differentiation are important moderators of this relationship, though not always in the hypothesized direction. Finally, there were important individual consequences for the role-structuring processes of role overlap and role switching.