Background: In the context of decreasing breastfeeding rates and unsuccessful breastfeeding promotion campaigns, a qualitative research project in the Northern part of the Netherlands was initiated. Objectives: As part of the overall project, the aim of this study was to explore the content and sources of breastfeeding knowledge among primiparous women. Identifying and categorizing the content and the sources of breastfeeding knowledge could guide professionals such as midwives and maternity nurses as well as others in the women’s surroundings to engage in disseminating knowledge and therefore support women in achieving their breastfeeding goals. Methods: We conducted 26 in-depth interviews from the emic perspective with 13 new mothers pre- and postpartum, up to saturation level. Transcripts were analysed applying thematic analysis. As sensitising concepts, the themes identified were divided into two categories: those gained from 'professional' sources and those obtained from 'popular' sources. Results: Five knowledge content themes were identified: (1) pros and cons of breastfeeding, (2) how breastfeeding works, (3) individual breastfeeding practice, (4) expressing milk, and (5) formula feeding. ‘Professional’ sources are perceived as more helpful than ‘popular’ sources, whereas ‘intuition’ was inductively identified as an important knowledge source. Conclusion: Limited breastfeeding practice exposure, along with the recommendations to breastfeed for six months and perceptions of breastfeeding as ‘natural’ at the same time, generates much pressure in women. Emphasizing all knowledge content in campaigns, addressing a variety of target groups in women’s social environment, and recognizing intuition as an adequate source of knowledge supported by professionals will facilitate women in making informed infant feeding decisions.