The Joint Video Team (JVT) of ISO/IEC MPEG and ITU-T VCEG are finalising a new standard for the coding (compression) of natural video images. The new standard [1] will be known as H.264 and also MPEG-4 Part 10, “Advanced Video Coding”. The standard specifies two types of entropy coding: Context-based Adaptive Binary Arithmetic Coding (CABAC) and Variable-Length Coding (VLC). This document provides a short introduction to CABAC. Familiarity with the concept of Arithmetic Coding is assumed (see chapter 8 of [2] for an introduction to Arithmetic Coding). Please note that the H.264 draft standard is not yet finalised and so readers are encouraged to refer to the latest version of the standard.