# What Is TLS (Transport Layer Security)? Definition and Examples > TLS (Transport Layer Security) is the IETF standard protocol that encrypts and authenticates network connections, including every HTTPS connection. Source: https://ssl.sh/glossary/tls/ Last updated: 2026-11-10 TLS is the successor to [SSL](https://ssl.sh/glossary/ssl/) and sits between TCP and an application protocol such as HTTP, SMTP or IMAP; QUIC reuses the TLS 1.3 handshake. A connection starts with a [handshake](https://ssl.sh/glossary/tls-handshake/) in which client and server agree on a version and cipher suite, the server proves its identity with an X.509 certificate, and both sides derive shared session keys. Application data is then encrypted and integrity-protected. The versions in use are TLS 1.2 (RFC 5246, 2008) and [TLS 1.3](https://ssl.sh/glossary/tls-1-3/) (RFC 8446, August 2018). ## Why it matters TLS protects passwords, cookies and API tokens from eavesdropping and tampering on untrusted networks, and certificate authentication stops an attacker from impersonating the server. Version choices matter: TLS 1.0 and 1.1 were removed from Chrome 84, Edge 84 and Firefox 78 in 2020 and formally deprecated by RFC 8996 in March 2021. TLS 1.3 removed static RSA key exchange and non-AEAD ciphers, so every TLS 1.3 connection has forward secrecy, and a full handshake needs one round trip instead of two. ## Example Check whether a server supports TLS 1.3: ```bash openssl s_client -connect example.com:443 -servername example.com -tls1_3