Even as most citizens of electoral democracies remain strongly committed to democratic values, most electoral democracies are suffering from democratic deficits that are eroding their legitimacy. There are deficits of inclusion, as elected governments often poorly represent those who are less educated or less wealthy or who belong to ethnic, religious, racial, or other minorities. There are deficits of deliberativeness, as governments fail to learn from experts and everyday citizens alike. And, increasingly, there are deficits of collective capacity, often the result of governments that are gridlocked by polarization and unable to marshal the political resources to address tough problems, such as climate change and migration. Democracies do, however, reinvent themselves, often by supplementing the legacy institutions of electoral democracy with innovative ways of deepening democracy. Among the most promising innovations are citizens’ assemblies, a kind of deliberative minipublic comprised of lay citizens selected through near-random methods to represent a broader public. These bodies are typically tasked with learning and deliberating about a problem and providing recommendations. In contrast to sitting legislatures, citizens’ assemblies are typically convened for a single issue or purpose, and they are closely defined in their mandate. As of 2020, there were over 20 cases of citizens’ assemblies, covering a range of issues (e.g., electoral reform, climate change, abortion, and urban planning), enabling some generalization about their capacities and promise. Owing to their high degree of representativeness of ordinary citizens, their capacities to learn and deliberate, and their abilities to break through difficult or gridlocked issues, citizens’ assemblies have considerable promise to address democratic deficits and to deepen democracy when they are carefully inserted into the political ecologies of modern democracies.