Since its launch in December 2015, Let’s Encrypt has steadily grown to become the largest CA in the Web PKI by certificates issued and the fourth largest known

Since its launch in December 2015, Let’s Encrypt has steadily grown to become the largest CA in the Web PKI by certificates issued and the fourth largest known CA by Firefox Beta TLS full handshakes. As of January 21, 2019, the CA had issued a total of 538M certificates for 223M unique FQDNs, and there were 91M unexpired Let’s Encrypt certificates valid for 155M unique FQDNs. This represents more unique certificates than all other CAs combined. (Except where otherwise noted, analysis in this section is based on data from that date. For Certificate Transparency data, we count certificates by the SHA-256 hash of the tbsCertificate structure after removing CT poison and SCTs to prevent double counting pre-certificates and certificates.)