A RAND study of teamwork-improvement initiatives in hospital labor and delivery (L&D) units was designed to document and learn from the experiences and outcomes of five L&D units as they implemented improvements in their teamwork practices over a one-year period. The study had two objectives: (1) better understand the conditions and actions required for hospital L&D units to achieve effective and sustainable teamwork practices, and (2) assess the extent to which successful adoption of teamwork practices may influence the experiences of L&D staff and patient outcomes. Substantial progress is possible in one year of implementing teamwork practices, which can improve proximal outcomes, such as staff knowledge and perceptions. More than a year of implementation effort is required to achieve a high level of performance on teamwork practices. Two dynamics might be involved in later years of implementation: (1) momentum from the first year might continue into later years, such that subsequent implementation might reinforce continued improvement, and (2) it might not be possible to sustain high intensity in implementation beyond the first year. The study results reinforce the importance of developing and implementing a well-crafted strategy by training staff in the L&D units, working consistently with staff to introduce practices, and providing coaching on effective use of practices. The study identified some key factors required by any given strategy for teamwork improvement, but it did not point to a standard template for implementation. This result implies that there may not be one fixed "intervention" that could be tested in comparative-control studies to develop further evidence for teamwork practices--