Reliable information about platforms’ content removal systems was, for many years, hard to come by. But data and disclosures are steadily emerging as researchers focus on the topic and platforms ramp up their transparency measures, including both self-regulatory efforts as well as disclosures required by law. This essay reviews the current and likely future sources of information. First, we discuss disclosures from platforms and other participants in content moderation, such as users and governments. Second, we discuss independent research from third parties such as academics and journalists, including data analysis, interviews and surveys. Finally, before concluding the essay, we list specific questions and areas for future empirical research.