Why are legislatures in some authoritarian regimes more powerful than others? Why does influence on policies and politics vary across dictatorships? To answer these questions, Lawmaking under Authoritarianism extends the power-sharing theory of authoritarian government to argue that autocracies with balanced factional politics have more influential legislatures than regimes with unbalanced or unstable factional politics. Where factional politics is balanced, autocracies have reviser legislatures that amend and reject significant shares of executive initiatives and are able to block or reverse policies preferred by dictators. When factional politics is unbalanced, notary legislatures may amend executive bills but rarely reject them, and regimes with unstable factional politics oscillate between these two extremes. Lawmaking under Authoritarianism employs novel datasets based on extensive archival research to support these findings, including strong qualitative case studies for past dictatorships in Argentina, Brazil, and Spain.