Authoring new content and updating existing content is an essential part of creating and maintaining a SNOMED CT® edition. Authoring high-quality SNOMED CT® content requires significant training and practice. The authoring process typically starts with a request for content to be added or updated in a specific SNOMED CT® edition. Once the request is approved and the requirements have been confirmed, the author will follow the appropriate editorial guidelines to create, update and/or inactivate the relevant concepts. Authoring is followed by careful manual review and automated validation. This chapter discusses the key principles of SNOMED CT® authoring and explores some tooling and training options.