This study focuses on family planning (FP) and its integration with childhood immunization services in five African countries, aiming to identify the mechanisms that make modern contraceptive methods (MCMs) acceptable to different communities. The research uses qualitative interpretive synthesis, guided by an analytical framework, to explore how context influences the acceptability of FP interventions. Through interviews and focus group discussions with key stakeholders, the study identifies empirical mechanisms that trigger acceptability and develops context-acceptability theories (CATs). These CATs detail the specific factors, such as religious beliefs, large family preferences, stigma, and male partner acceptance, that influence whether FP interventions are accepted in different contexts.