Substack is a platform that enables writers to publish and monetize their newsletters. The company was founded in 2017 and is headquartered in San Francisco, California. Substack provides tools for writers to manage their subscriber lists, design their newsletters, and process payments. The platform allows writers to keep a larger share of their subscription revenue than traditional media companies, and has been used by a number of high-profile journalists and writers. Substack has raised over $15 million in funding from investors including Andreessen Horowitz and Y Combinator.