Implementation Science (IS) is a new branch of health services research (HSR) that strives to increase the efficiency and effectiveness of health care quality improvement (QI) efforts. Despite the fact that IS takes a systems approach, building contextual factors into its research designs, the complex systems context of IS itself-and the impact this context has on IS practice-has never been scrutinized. Using individual interviews and participant observation, the research described here characterizes key contextual factors affecting how implementation scientists in one large health care organization approach and conduct their research. Some of the organizational and professional system forces structuring their attitudes and actions were grant-related time lines, administrative burdens, and team turnover. The need for publications also figured highly. While such pressures (and related responses to them) may be rife in most grant-funded health care research settings, IS's particularly marginal position drove these implementation scientists to strategically highlight particular aspects of their work depending on which audience or part of the system they required favor from. Their narratives illuminate the contradictions and contests entailed within and engendered by organizational and professional structures, and the strategies used to negotiate these. They also reveal a great deal about the struggles underwriting disciplinary identity claims in a complex systems context.