Media Newsletters Are Booming, and Substack’s Co-Founders Lit the Fuse

Last year, Substack’s only employees were its three co-founders: Hamish McKenzie, Chris Best and Jairaj Sethi. Now, the San Francisco-based startup has a bigger team—it’s up to 18 employees—and even bigger ambitions: trying to do nothing less than reinvigorate the flagging media industry.