This study examines collaboration between public librarians and speech and language therapists within the initiative Språkpiller, in which books are prescribed by speech and language therapists and distributed through public libraries to support children with language difficulties. Although collaborations between libraries and healthcare services in language promoting initiatives are relatively common in Sweden, research focusing on the professional perspectives of the actors involved remains limited. The study adopts a professional theory perspective to explore how librarians and speech and language therapists describe and understand their collaboration. Particular attention is paid to questions of jurisdiction, professional knowledge traditions and quality. Empirically, the study is based on qualitative semi-structured interviews with librarians and speech and language therapists involved in Språkpiller. The findings suggest that the professions operate within partly different jurisdictions and knowledge domains, but that these are generally experienced as complementary rather than competitive. Librarians primarily emphasise expertise in children’s literature, reading promotion and literary quality, while speech and language therapists stress knowledge of atypical language development and language intervention. Differences in terminology, perspectives and professional traditions occasionally create tensions, particularly regarding the role of books in the intervention, but the collaboration is nevertheless characterised by negotiation, compromise and mutual respect. The study further indicates that collaboration facilitates knowledge exchange between the professions and may strengthen the perceived quality of professional practice by combining medical, pedagogical and literature-promoting perspectives. At the same time, participants report having limited knowledge of how the collaboration influences children’s language development over time.