Messaging Layer Security (MLS) is a modern messaging protocol for end-to-end encryption. MLS is a security layer for encrypting messages in groups of any size. It is designed to be efficient, practical, and secure. The MLS working group of the Internet Engineering Task Force maintains MLS. The idea for MLS was initiated by Wire, Mozilla, and Cisco in 2016. Other contributors include the University of Oxford, Facebook, INRIA, Google, and Twitter. Google is adopting the MLS protocol for its Messages app. The latest specification allows for interoperability across messaging services, including WhatsApp, Messenger, and Google Messages.