In this study, we explored how rates of involuntary hospitalization on psychiatric grounds varied across 22 countries in Western Europe, Australia, and New Zealand between 2008 and 2017. Alongside this, we also compared national legislation and investigated whether variations in rates could be explained by national-level socioeconomic, demographic, and clinical factors. It was conducted by members of the NIHR Mental Health Policy Research Unit and was commissioned by the independent review of the Mental Health Act (1983) in England and Wales in 2017–2018. For us as researchers, this was an unusual project to work on: there are few other studies in this area, and we had to collect a large body of information about the different involuntary hospitalization legislations and their application in practice. We worked with a solicitor to do this, but there were still significant challenges, such as language barriers and understanding the technicalities of the different legislations. We relied heavily on the expertise of “key informants”: mental health law academics or practicing psychiatrists based in each of the countries. Meanwhile, the project also posed many other interesting research methods questions, such as how to analyze the relationship between rates of involuntary hospitalization and legislation. We also learnt a lot about the complexities of obtaining and using these types of publicly available data, especially in terms of its accessibility and limitations. Overall, this was an interesting project to work on, and one that we hope will help provide a platform for future work on this topic.