Tarleton Gillespie’s Custodians of the Internet argues that social media platforms are not neutral conduits for public expression but powerful socio-technical institutions that actively shape what can be seen, said, amplified, hidden, or removed online. His central claim is that all platforms moderate, despite their frequent rhetorical commitment to openness, neutrality, and democratic participation. The case of Facebook’s removal of Nick Ut’s “Napalm Girl” photograph illustrates the difficulty of moderation: the image was simultaneously historically indispensable and formally in breach of policies concerning child nudity, revealing how platform rules often collide with cultural, ethical, and journalistic value. Gillespie therefore reframes moderation not as a peripheral housekeeping function but as a constitutive act of platform governance. Platforms must intervene to limit abuse, pornography, violence, harassment, terrorism, and illegality; yet every intervention risks accusations of censorship, bias, or cultural insensitivity. This produces a profound contradiction: platforms depend commercially and ideologically on appearing open, while their survival depends on continuous curation, judgement, and enforcement. Gillespie’s analysis also exposes the hidden human labour behind moderation, challenging the myth that algorithmic systems alone manage online disorder. Ultimately, the book demonstrates that moderation is not merely a technical problem of scale but a political problem concerning legitimacy, accountability, and public power. If platforms now organise much of contemporary public discourse, then their rules, labour practices, and enforcement systems must be scrutinised as forms of private governance with public consequences.