The Decade of Vaccines Collaboration (DoVC) Research and Development (R&D) Working Group identified implementation research as an important step toward achieving high vaccine coverage and the uptake of desirable new vaccines. The R&D Working Group noted that implementation research is highly complex and requires participation of stakeholders from diverse backgrounds to ensure effective planning, execution, interpretation, and adoption of research outcomes. Unlike other scientific disciplines, implementation research is highly contextual and depends on social, cultural, geographic, and economic factors to make the findings useful for local, national, and regional applications. This paper presents the broad framework for implementation research in support of immunization and sets out a series of research questions developed through a Delphi process (during a DoVC-supported workshop in Sitges, Spain) and a literature review.