Description: Fake news, conspiracies, manipulated media, selective reporting, facts derided as lies: citizens of democracies encounter wildly conflicting information about the supposedly factual world. Think of Pizzagate, a well-known and extensively discredited conspiracy theory about an abuse circle run by high-ranking Democratic Party officials. Or of the recent 2020 United States presidential election, where most Republican voters said they believed that Trump won and the official results were fraudulent. COVID-19 has produced its own myriad of false beliefs, for example that the virus was engineered in China. Even outright denials of the pandemic or other complex phenomena such as climate change are not uncommon. The borders between fact and opinion are blurring, and the prospects of deliberative democracy and collective action become increasingly bleak. Of course, truth has always been precarious - neither misinformation nor widespread false beliefs are unique to our time. But the web and social media technologies have distinctly rearranged the struggles over truth and falsehood. Through its unfiltered publication process, breakneck pace, and obsession with engagement (rather than accuracy), the modern web has created not only decentralized modes of expression but also novel vectors for misinformation and disinformation. We therefore need new tools, concepts and technologies to ensure the integrity of information ecosystems. This workshop aims to bring together leaders across industry and academia to discuss what tools for measurement and mitigation could look like.