We present a formal model of government control of the media to illuminate variation in media freedom across countries and over time. Media bias is greater and state ownership of the media more likely when the government has a particular interest in mobilizing citizens to take actions that further some political objective but are not necessarily in citizens' individual best interest; however, the distinction between state and private media is smaller. Large advertising markets reduce media bias in both state and private media but increase the incentive for the government to nationalize private media. Media bias in state and private media markets diverge as governments become more democratic, whereas media bias in democracies and autocracies converge as positive externalities from mobilization increase.
