This reference guide on Organization presents the critical features to be considered in designing the organizational arrangements for a tax administration. It sets out the general principles and good practice of organizational design and describes common organizational structures adopted by tax administrations. It is important to note that organizational design is more than changing the organizational chart - it facilitates thinking on how, where, and when work across an organization is done. This guide is divided into six chapters highlighting the framework for organizational design, organizational models, the role of headquarters, field operations, and specialized units as well as the impact of new tax administration responsibilities on organizational design. It is part of a series of Virtual Training to Advance Revenue Administration (VITARA) reference guides that have been developed based on the content of the VITARA online modules.