The concept of a bundle as a way to implement multiple best practices together to support quality improvement and better patient outcomes has great appeal.^1,2 However, little is known about how bundles work and whether the individual components or the group are most important to care improvement. In this issue of JAMA Internal Medicine, Klompas and colleagues³ demonstrate that individual components of a bundle to lower rates of ventilator-associated pneumonia may have different effects on the outcome.

Bundles are a key component of several large-scale improvement collaborations.^1,2 In general, the bundling concept encourages complete adherence to a set of best practices that should be administered to every patient, every time. In many ways, the bundle parallels the use of checklists as an approach to standardizing care in a clinically useful and team-oriented approach. Components of care bundles are chosen based on best available evidence, ideally derived from high-quality randomized clinical trials. Even if individual components vary in terms of strength of evidence, a key aspect of bundling is that the whole of the bundle is greater (potentially) than the sum of its parts. Synergy of the components, or even the overall effectiveness of the bundle, could result because the effort put into implementing a bundle galvanizes other critical changes in care teams, communication, or organizational priorities important to improving patient outcomes. Alternatively, the bundle approach could be a key precondition for an implementation (and, potentially, measurement) strategy, including education, audit and feedback, and process redesign.