Abstract Background Breastfeeding is good for both baby and mother, and the associated health benefits persist. However, in many communities breastfeeding is not the norm. Financial incentives are a potentially powerful method to achieve health-related behaviour change, and these incentives have been used with varying success in a range of settings. The use of financial incentives to promote breastfeeding is controversial, and there has been little research in this area. A street intercept survey with women from areas of low breastfeeding rates showed that financial incentives were acceptable to 80% (95% CI 67–88; n=54) of those sampled. In this study, we aimed to investigate in depth the acceptability of financial incentives for breastfeeding both in principle and in practice among a range of key stakeholders. Our research is part of a wider study to develop and trial a financial incentive scheme for breastfeeding in areas with 6–8-week rates below 40%. Methods We undertook semistructured individual interviews (n=54) and focus groups (n=8) with two stakeholder groups based in south Yorkshire and north Derbyshire: mothers who had breastfed or formula fed, or both (n=38) and health-care staff with infant feeding roles (n=53). A sampling frame was developed to purposively sample for maximum variation in the range of infant feeding preferences and experiences in different age groups. Stakeholders were recruited from children's centres, breastfeeding support groups, parent and toddler groups, and community or hospital maternity services. Health-care staff were midwives, health visitors, breastfeeding peer support workers, children's centre managers, charity or voluntary sector workers, public health leads, and commissioners. Interviews were analysed by thematic analysis, drawing on the principles of framework analysis. NVivo was used to support the analytical process. Interviewer bias was minimised by use of inter-rater reliability, peer debriefing, and reflexivity. Ethics approval for the study was obtained from ScHARR Research Ethics Committee, NHS R&D, and Sheffield Local Authority Research Governance. Findings Although a wide range of views about financial incentives were expressed, both mothers and health-care staff had similar views about the potential benefits, emotional effect, and ethical implications of a financial incentive scheme. The common key emergent themes were the scheme's potential to encourage, reward, and support breastfeeding; ethical concerns about financial incentives for breastfeeding; potential negative effects; and concerns about the practical implementation of a scheme. Many interviewees felt that financial incentives might encourage more women to attempt breastfeeding. Health-care staff, particularly, felt that a financial incentive might help to normalise breastfeeding in communities with low breastfeeding rates. Some viewed the incentive as being a reward for breastfeeding and that breastfeeding would be perceived as valuable and good. Both groups were concerned about moral implications, perception of incentives as bribery, penalising those unable to breastfeed, and how such interventions would be policed. Many considered the moral implications of how a financial incentive would be spent and whether the incentive should be cash or vouchers. Further, financial incentives could affect women negatively—in particular, if it reduced the intrinsic motivation to breastfeed. Additionally, an incentive could add pressure on the woman to breastfeed and might not help if she ran into difficulties. Both groups made suggestions for the practical implementation of the scheme that would make it more acceptable. There was low acceptability for verification methods that required the mother to perform in order to prove that she was breastfeeding. Interpretation There was difficulty in recruiting primiparous women to the study, which limits the generalisability of these results. Although a wide range of views were expressed within and between stakeholder groups, financial incentives for key stakeholders were broadly acceptable, in principle. Issues were identified that need consideration when implementing a financial incentive scheme in practice. Funding Medical Research Council—National Prevention Research Initiative (MR/J000434/1).