OBJECTIVE National guidelines recommend that all children under age six receive fluoride varnish (FV) in medical settings. However, application rates remain low. This study aimed to update understanding of barriers and facilitators to guideline concordant FV application. METHODS We conducted virtual semi-structured interviews with a purposive sample (eg, FV application rates, geographic location, practice size and type) of pediatric primary care clinicians and medical assistants in Massachusetts between February 1 and June 30, 2022. The Consolidated Framework for Implementation Research (CFIR) served as the study's theoretical framework and data were analyzed using a modified grounded theory approach. RESULTS Of the 31 participants, 90% identified as White and 81% as female. Major themes, which linked to four CFIR domains, included: variation in perceived adequacy of reimbursement; differences in FV application across practice types; variation in processes, protocols, and priorities; external accountability for quality of care; and potential levers for change. Important subthemes included challenges for small practices; role of quality measures in delivering guideline-concordant preventive oral health care; and desire for preventive care coordination with dentists. CONCLUSIONS This study suggests that potential barriers and facilitators to guideline concordant FV application exist at multiple levels that may warrant further study. Examples include testing the effectiveness of quality measures for FV application and testing strategies for implementing consistent processes and protocols for improving FV application rates.