Substack is an American online platform that provides publishing, payment, analytics, and design infrastructure to support subscription newsletters.

[9][10] Best and McKenzie describe Ben Thompson's Stratechery, a subscription-based tech and media newsletter, as a major inspiration for their platform.

[15] The New York Times columnist Mike Isaac argued in 2019 that companies like Substack see newsletters as a more stable means to maintain readers through a more direct connection with writers.

[16] As of late 2020, large numbers of journalists and reporters were coming to the platform, driven in part by the long-term decline in traditional media (there were half as many newsroom jobs in 2019 as in 2004).

[17] Around that time, The New Yorker wrote that while "Substack has advertised itself as a friendly home for journalism, ... few of its newsletters publish original reporting; the majority offer personal writing, opinion pieces, research, and analysis.

[19][20] Major writers using Substack include historian Heather Cox Richardson, tech journalists Casey Newton[21] and Eric Newcomer,[22] journalist Matthew Yglesias,[23] economists Glenn Loury and Emily Oster, linguist John McWhorter, journalists Matt Taibbi and Bari Weiss,[24] and authors Daniel M. Lavery, George Saunders, Blake Nelson, Chuck Palahniuk,[25] Marianne Williamson,[26] Salman Rushdie,[27] Tui T. Sutherland,[28] David Bentley Hart,[29] and Skottie Young.

[38] Substack raised an initial seed round in 2018 from investors including The Chernin Group, Zhen Fund, Twitch CEO Emmett Shear, and Zynga co-founder Justin Waldron.

[9] Substack expanded into comics content in 2021 and signed creators including Saladin Ahmed, Jonathan Hickman, Molly Ostertag, Scott Snyder, and James Tynion IV, paying them while keeping their subscription revenue.

[38] By late 2020, the conservative newsletter The Dispatch claimed the title of top Substack user, with more than 100,000 subscribers and over $2 million in first-year revenue, according to founder Steve Hayes.

The Washington Post mentioned Joseph Mercola (whose content Imran Ahmed, CEO of the Center for Countering Digital Hate, called "so bad [that] no one else will host it") and Steve Bannon (whom Elizabeth Dwoskin, writing for The Washington Post, accused of spreading "violent rhetoric and false claims about the [2020] election in the weeks leading up to the Capitol siege on Jan. 6") as conspiracy theorists who have moved their online presence to Substack.

[48] In January 2022, the Center for Countering Digital Hate accused Substack of allowing content that could be dangerous to public health.

The Center estimated that the company earned $2.5 million per year from the top five anti-vaccine authors alone (who have tens of thousands of subscribers).

[51] Substack CEO Hamish McKenzie responded to the controversy by confirming that the company will continue to allow the publication of extremist views, saying that attempting to censor them would make the problem worse.