Embodiments of the disclosure relate to methods, apparatus and systems for authentication of a user. The described embodiments relate to obtaining ear biometric data for a user to be authenticated. The ear biometric data comprises one or more features characteristic of the user's ear canal and an associated fit metric indicative of a positioning of a personal audio device relative to the user's ear canal, the personal audio device comprising a transducer for application of acoustic stimulus to the user's ear to obtain the ear biometric data. The user may be identified as a particular authorised user based on one or more features and the associated fit metric.