The collaboration between users and developers has been considered an important success factor for information system (IS) development. However, the new context of enterprise systems calls for further research in the collaboration of consultants and users when they work together to implement those commercial packages. This study introduces the concept of boundary spanning expertise, and examines how such expertise contributes to consultant-user collaboration during enterprise system implementations. Data analysis suggest that having overlapping knowledge, legitimate participation and interest in engaging two parties are only necessary conditions for a novice boundary spanner. To become an expert in boundary spanning, one should be able to probe and to challenge a status-quo when helping both parties overcome knowledge barriers. The study contributes to IS and project management theory by developing a domain-specific conceptualization of boundary spanning expertise. Findings of this study offer practical insights into staffing and managing cross-functional knowledge teams.