A large and growing proportion of the world’s population rely on shared sanitation facilities. These have historically been excluded from international sanitation targets due to concerns about acceptability, hygiene and access. With the development of new targets and indicators for the Sustainable Development Goals, it has been proposed to include shared facilities as ‘improved’ sanitation based on the number of users, if the facility is of an ‘improved’ technology and if the users are known to each other. The aim of this research was threefold: i) to provide an overview of the available evidence on shared sanitation and outcomes related to health, access, use, operation and maintenance, gender and cost, ii) to describe the geographic and demographic scope of shared sanitation globally, and iii) to develop and pilot methods exploring factors that may explain any increased risk of adverse health outcomes associated with shared sanitation. Results from a systematic literature review on shared sanitation and health showed that households accessing shared sanitation facilities were more likely to suffer from ill-health, specifically diarrhoea. However, the methodological quality of the available studies was limited. The global analysis of household survey data showed that households sharing sanitation facilities were poorer, less educated and more likely to live in urban areas. The majority of households accessing shared sanitation were found in Africa and South-East Asia. The results from the literature review and household survey data led to the development of a cross-sectional study in Orissa, India. This study aimed to assess differences in shared and private sanitation access in 30 slums—both in terms of the users and the actual facilities. Results from this study show that households accessing shared sanitation were poorer, less educated and less likely to have water access in or near their home. In addition, significant differences in terms of cleanliness and presence of water were observed between private and shared facilities. Users of shared sanitation were more likely to continue practicing open defecation and significantly more cases of diarrhoea were reported by individuals living in these households. The underlying reasons for this potential increased risk of disease for users of shared sanitation are not clear, but the type of users, cleanliness of facilities and opportunities to practice good hygiene are all expected to play a role. As such, these factors may also be of importance, in addition to the number of users and sanitation technology, if a shared sanitation facility is expected to be considered ‘improved’ sanitation in future monitoring targets.