In this research, we disentangle the relationship between several key aspects of a team leader's experience and the likelihood of improvement project success. Using the lens of socio-technical systems, we argue that the effect of team leader experience derives from the social system as well as the technical system. The aspects of team leader experience we examine include team leader social capital (a part of the social system) and team leader experience leading projects of the same type (a part of the technical system).We examine four different, yet related, dimensions of a team leader's social capital, which we motivate based on the social networks literature. One dimension, team leader familiarity, suggests that social capital is created when team leaders have experience working with current team members on prior improvement projects, and that such social capital increases the likelihood of improvement project success. We develop three additional dimensions, using social network analysis (SNA), to capture the idea that the improvement team leader's social capital extends beyond the current team to include everyone the leader has previously worked with on improvement projects. Contrasting our SNA-based dimensions with team leader familiarity enables us to better understand the impact of a team leader's social capital both inside and beyond the team. We also examine the effect of a team leader's experience leading prior projects of the same type, and consider the extent to which organizational experience may moderate the impact of both team leader social capital and same-type project experience.Based on analysis of archival data of six sigma projects spanning six years from a Fortune 500 consumer products manufacturer, we find that two of our SNA-based dimensions of team leader social capital, as well as experience leading projects of the same type, increase the likelihood of project success.In addition, we show that organizational experience moderates the relationship between team leader same-type project experience and project success. However, this is not the case for the relationship between the dimensions of team leader social capital and project success. These results provide insights Page 3 of 55 A c c e p t e d M a n u s c r i p t 3 regarding how dimensions of team leader experience and organizational experience collectively impact the operational performance of improvement teams.