This Practice Note explores age assurance in online environments, emphasising its importance for compliance with a number of legal frameworks. It provides a practical introduction to age verification and age estimation methods and associated technologies. It highlights their role in compliance with legal frameworks like the United Kingdom General Data Protection Regulation, Assimilated Regulation 2016/679 (UK GDPR) and the Online Safety Act 2023, among others. It also provides an overview of the global context, and discusses key enforcement actions and the role of stakeholders in implementing age-appropriate measures, including those aimed at the protection of children.