 (SDO) in- volved in telecommunications and synchronization. It includes an overview of their organizational structures and the processes they use to define standards. For each SDO, the chapter also outlines its contribution to time synchronization specifications and standards. This chapter also introduces some of the telecom groups and industry alliances that contribute to the open interfaces and disaggregation architecture supporting the 5th generation (5G) radio access net- work (RAN). Many of the details on the standards themselves are covered in the following chapters. This chapter is focused on those SDOs whose area of interest and the contributions they make in- volve either time synchronization or mobile architectures, or both. Understanding the position these SDOs take, and their role in defining standards, should help you to understand the purpose of each standard as well as the customer requirements or architectural problem that the standard is meant to address. Innovators, organizations, and industries benefit from having a common definition that simplifies transactions, allows interoperability, and enables people to work toward common goals. SDOs, also known as standards setting organizations (SSO), define and maintain standards to meet industry needs. The terms SDO and SSO are widely used interchangeably. SDOs are organizations that focus on developing, maintaining, amending, and publishing technical standards using open and transparent processes. Some SDOs are large, formally recognized organiz- ations with a global membership consisting of national representatives (public or private)-al- though companies and individuals may also participate. Others are based on a community of profes- sionals with or without a formal membership. Still others are organizations that support or certify standards developed elsewhere and may even author none themselves. There are standards bodies at the international, regional, and national levels. For example, the Inter- national Telecommunication Union (ITU) is an int