In 2011, the Veterans Health Administration (VHA) implemented electronic consults (e-consults) as an alternative to in-person specialty visits to improve access and reduce travel for veterans. We conducted an evaluation to understand variation in the use of the new e-consult mechanism and the causes of variable implementation, guided by the Consolidated Framework for Implementation Research (CFIR).Qualitative case studies of 3 high- and 5 low-implementation e-consult pilot sites. Participants included e-consult site leaders, primary care providers, specialists, and support staff identified using a modified snowball sample.We used a 3-step approach, with a structured survey of e-consult site leaders to identify key constructs, based on the CFIR. We then conducted open-ended interviews, focused on key constructs, with all participants. Finally, we produced structured, site-level ratings of CFIR constructs and compared them between high- and low-implementation sites.Site leaders identified 14 initial constructs. We conducted 37 interviews, from which 4 CFIR constructs distinguished high implementation e-consult sites: compatibility, networks and communications, training, and access to knowledge and information. For example, illustrating compatibility, a specialist at a high-implementation site reported that the site changed the order of consult options so that all specialties listed e-consults first to maintain consistency. High-implementation sites also exhibited greater agreement on constructs.By using the CFIR to analyze results, we facilitate future synthesis with other findings, and we better identify common patterns of implementation determinants common across settings.