A burgeoning literature studies compulsory voting and its effects on turnout, but we know very little about how compulsory voting works in practice. In this Element, the authors fill this gap by providing an in-depth discussion of compulsory voting rules and their enforcement in Australia, Belgium, and Brazil. By analysing comparable public opinion data from these three countries, they shed light on citizens' attitudes toward compulsory voting. The Element examines citizens' perceptions, their knowledge of the system, and whether they support it. The authors connect this with information on citizens' reported turnout and vote choice to assess who is affected by mandatory voting and why. The work clarifies that there is no single system of compulsory voting. Each country has its own set of rules, and most voters are unaware of how they are enforced.