  Moderating user-generated content on online platforms is crucial for
balancing user safety and freedom of speech. Particularly in the United States,
platforms are not subject to legal constraints prescribing permissible content.
Each platform has thus developed bespoke content moderation policies, but there
is little work towards a comparative understanding of these policies across
platforms and topics. This paper presents the first systematic study of these
policies from the 43 largest online platforms hosting user-generated content,
focusing on policies around copyright infringement, harmful speech, and
misleading content. We build a custom web-scraper to obtain policy text and
develop a unified annotation scheme to analyze the text for the presence of
critical components. We find significant structural and compositional variation
in policies across topics and platforms, with some variation attributable to
disparate legal groundings. We lay the groundwork for future studies of
ever-evolving content moderation policies and their impact on users.
