This International Standard defines the structure and the data elements of Authentication Context for Biometrics (ACBio), which is used for checking the validity of the result of a biometric verification process executed at a remote site. This International Standard allows any ACBio instance to accompany any data item that is involved in any biometric process related to verification and enrolment. The specification of ACBio is applicable not only to single modal biometric verification but also to multimodal fusion. This International Standard specifies the cryptographic syntax of an ACBio instance. The cryptographic syntax of an ACBio instance is based on an abstract Cryptographic Message Syntax (CMS) schema whose concrete values can be represented using either a compact binary encoding or a human-readable XML encoding. This International Standard does not define protocols to be used between entities such as BPUs, claimant, and validator. Its concern is entirely with the content and encoding of the ACBio instances for the various processing activities.