A state-of-the-art account of what we know and do not know about the effects of digital technology on democracy.

1. Introduction Nathaniel Persily and Joshua A. Tucker; 2. Misinformation, Disinformation, and Online Propaganda Andrew M. Guess and Benjamin A. Lyons; 3. Social Media, Echo Chambers, and Political Polarization Pablo Barbera; 4. Online Hate Speech Alexandra A. Siegel; 5. Bots and Computational Propaganda: Automation for Communication and Control Samuel C. Woolley; 6. Online Political Advertising in the United States Erika Franklin Fowler, Michael M. Franz, and Travis N. Ridout; 7. Democratic Creative Destruction? The Effect of a Changing Media Landscape on Democracy Rasmus Kleis Nielsen and Richard Fletcher; 8. Misinformation and Its Correction Chloe Wittenberg and Adam J. Berinsky; 9. Comparative Media Regulation in the US and Europe Francis Fukuyama and Andrew Grotto; 10. Facts and Where to Find Them: Empirical Research on Internet Platforms and Online Speech Daphne Keller and Paddy Leerssen; 11. Dealing with Disinformation: Evaluating the Case for CDA 230 Amendment Tim Hwang; 12. Democratic Transparency in the Platform Society Robert Gorwa and Timothy Garton Ash; 13. Conclusion: The Challenges and Opportunities for Social Media Research Nathaniel Persily and Joshua A. Tucker.