Let’s Encrypt is a free, automated, and open certificate authority (CA) operated by the Internet Security Research Group (ISRG). It launched publicly in April 2016 with a mission to make encrypted HTTPS connections the default for the entire web.
Before Let’s Encrypt, getting an SSL/TLS certificate meant paying $10-$100+ per year and going through a manual validation process. This cost and complexity meant that a huge portion of the web ran unencrypted. Let’s Encrypt eliminated both barriers by providing certificates at zero cost through an automated protocol called ACME (Automatic Certificate Management Environment).
The impact has been dramatic. Let’s Encrypt has issued over 4 billion certificates since launch and currently serves more than 360 million websites. The percentage of web traffic using HTTPS jumped from around 40% in 2016 to over 80% by 2023, and Let’s Encrypt deserves a large share of that credit.
Certbot, developed by the Electronic Frontier Foundation, is the most popular client for obtaining and renewing Let’s Encrypt certificates. Certificates are valid for 90 days and are designed to be renewed automatically. Major hosting providers, CDNs, and platforms like Cloudflare, AWS, and cPanel have built in direct Let’s Encrypt support.
The ISRG is headquartered in San Francisco and funded by corporate sponsors including Mozilla, Cisco, Google, Meta, and the EFF. The organization runs on a small staff of about 30 people — remarkable given the scale of the operation. Let’s Encrypt also inspired the ISRG to launch Prossimo, a project to move critical internet infrastructure to memory-safe code.
