The current edition of the Overview of Tax Administrations in CIAT Countries (Volume I) has been prepared using data from the latest version of the International Survey on Revenue Administration (ISORA), collected for 179 countries in 2023 and reflecting the situation of tax administrations in 2022. The survey covers: 1) administered instruments, revenue collection, and budgets; 2) available human resources; 3) organization and operational functions (segmentation and registration of taxpayers, taxpayer assistance and services, filing and payment of obligations, enforced debt collection, and audit and tax control activities); and 4) innovative techniques and information and communication technologies (ICT) applied to tax administration and improving tax compliance.