The SAGE Working Group on Vaccine Hesitancy has defined vaccine hesitancy as the delay in acceptance or refusal of vaccination despite the availability of vaccination services. This definition emphasizes that vaccine hesitancy is complex, context-specific, and influenced by factors such as complacency, convenience, and confidence. The Working Group chose the term "vaccine" over "vaccination" hesitancy to maintain a broader scope, although the latter term more accurately captures a wider range of immunization concerns. The Vaccine Hesitancy Determinants Matrix categorizes factors affecting the behavioral decision to accept, delay, or reject vaccines into three categories: contextual, individual and group, and vaccine/vaccination-specific influences. The matrix includes determinants identified from research, field experiences, and expert discussions. The Working Group also noted that poor communication can negatively influence vaccination uptake and contribute to vaccine hesitancy, but it is not a specific determinant. The definition aims to provide a standard term for Immunization Programme Managers, policymakers, clinicians, and researchers to consistently address the broad range of factors causing low vaccination uptake.The SAGE Working Group on Vaccine Hesitancy has defined vaccine hesitancy as the delay in acceptance or refusal of vaccination despite the availability of vaccination services. This definition emphasizes that vaccine hesitancy is complex, context-specific, and influenced by factors such as complacency, convenience, and confidence. The Working Group chose the term "vaccine" over "vaccination" hesitancy to maintain a broader scope, although the latter term more accurately captures a wider range of immunization concerns. The Vaccine Hesitancy Determinants Matrix categorizes factors affecting the behavioral decision to accept, delay, or reject vaccines into three categories: contextual, individual and group, and vaccine/vaccination-specific influences. The matrix includes determinants identified from research, field experiences, and expert discussions. The Working Group also noted that poor communication can negatively influence vaccination uptake and contribute to vaccine hesitancy, but it is not a specific determinant. The definition aims to provide a standard term for Immunization Programme Managers, policymakers, clinicians, and researchers to consistently address the broad range of factors causing low vaccination uptake.