Background: People with profound intellectual disabilities represent a vulnerable and heterogeneous population whose health-related needs and questions often remain unheard. One reason for this is that they are usually unable to participate in verbal communication. However, there is also a lack of suitable approaches to communicate health-related information to them according to their capabilities. The research presented in this paper addresses this gap. Methods: Following grounded theory methodology, we used a multimethod approach. Based on a theoretical analysis, a Delphi study (n = 14) was conducted as a starting point to map the research field. In a second step, these findings were incorporated into an online survey targeting disability care professionals (n = 111). Three field studies supplemented the data, encompassing a variety of ethnographic methods. Results: People with PIMD have basic health-related capabilities that can improve their health literacy. Nevertheless, their support environments have to take over many health literacy-related requirements by proxy or substitution. One of the most important tasks is to engage health information in an individualised way. Conclusions: The findings underline the importance of focusing on more basic capabilities and intersubjective approaches in health literacy research and practice, especially regarding new perspectives on the inclusion of previously marginalised populations (such as people with PIMD).