On September 14, 2015, our first publicly-trusted certificate went live. We were proud that we had issued a certificate that a significant majority of clients could accept, and had done it using automated software. Of course, in retrospect this was just the first of billions of certificates. Today, Let’s Encrypt is the largest certificate authority in the world in terms of certificates issued, the ACME protocol we helped create and standardize is integrated throughout the server ecosystem, and we’ve become a household name among system administrators. We’re closing in on protecting one billion web sites.
In 2023, we marked the tenth anniversary of the creation of our nonprofit, Internet Security Research Group, which continues to host Let’s Encrypt and other public benefit infrastructure projects. Now, in honor of the tenth anniversary of Let’s Encrypt’s public certificate issuance and the start of the general availability of our services, we’re looking back at a few milestones and factors that contributed to our success.
Growth
A conspicuous part of Let’s Encrypt’s history is how thoroughly our vision of scalability through automation has succeeded.
In March 2016, we issued our one millionth certificate. Just two years later, in September 2018, we were issuing a million certificates every day. In 2020 we reached a billion total certificates issued and as of late 2025 we’re frequently issuing ten million certificates per day. We’re now on track to reach a billion active sites, probably sometime in the coming year. (The “certificates issued” and “certificates active” metrics are quite different because our certificates regularly expire and get replaced.)
The steady growth of our issuance volume shows the strength of our architecture, the validity of our vision, and the great efforts of our engineering team to scale up our own infrastructure. It also reminds us of the confidence that the Internet community is placing in us, making the use of a Let’s Encrypt certificate a normal and, dare we say, boring choice. But I often point out that our ever-growing issuance volumes are only an indirect measure of value. What ultimately matters is improving the security of people’s use of the web, which, as far as Let’s Encrypt’s contribution goes, is not measured by issuance volumes so much as by the prevalence of HTTPS encryption. For that reason, we’ve always emphasized the graph of the percentage of encrypted connections that web users make (here represented by statistics from Firefox).
(These graphs are snapshots as of the date of this post; a dynamically updated version is found on our stats page.) Our biggest goal was to make a concrete, measurable security impact on the web by getting HTTPS connection prevalence to increase—and it’s worked. It took five years or so to get the global percentage from below 30% to around 80%, where it’s remained ever since. In the U.S. it has been close to 95% for a while now.
A good amount of the remaining unencrypted traffic probably comes from internal or private organizational sites (intranets), but other than that we don’t know much about it; this would be a great topic for Internet security researchers to look into.
We believe our present growth in certificate issuance volume is essentially coming from growth in the web as a whole. In other words, if we protect 20% more sites over some time period, it’s because the web itself grew by 20%.
A few milestones
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