Interprofessional collaboration (IPC) in healthcare is regarded as important by professionals, as it increases the quality of care while decreasing costs. Interprofessional education (IPE) is a prerequisite for IPC and influences learners' attitudes, knowledge, and collaboration skills. Since attitudes shape behavior, understanding how they are formed is crucial for influencing IPC in learners' professional practice. We investigated what kind of IPE works, for which students, how, and in what circumstances to develop positive attitudes towards IPC. Using realist synthesis, we extracted causal mechanisms that produce positive attitude outcomes and the conducive contexts that trigger them. Our analysis resulted in six plausible context-mechanism-outcome configurations that explain positive attitude development. Positive IPC attitudes are more likely to arise in contexts where IPE provides time and facilities for formal and informal interactions, as this allows learners to get to know each other both professionally and personally, fostering trust, respect, and mutual liking. Additionally, positive attitudes are more likely in contexts where the IPE curriculum is perceived as career-relevant and boosts confidence. Key mechanisms of positive attitude development include getting to know the other learners professionally and personally, experiencing positive affect during IPE, and learners experiencing mutual dependence. Sustained positive attitudes are more likely to develop when there is organizational support for IPC and professionals attend IPE on an ongoing basis, allowing the attitudes and values expected in IPC to be positively reinforced and eventually integrated into the learners' personal value system.