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SNOMED CT is designed to allow the International Edition to be enhanced by adding Extensions that address national or local requirements. Additional content required to support national, local or organizational needs that may not have international relevance or may not meet the editorial guideline for inclusion in the International Edition.
SNOMED CT design also includes the Reference Set mechanism which provides a standard way to customize and enhance content for use in a particular languageparticular  language, specialty, application or context. Reference Sets developed nationally or locally can modify search and display of content from the International Edition as well as enhancing Extension content.

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Many clinical concepts are relevant in all countries, organizations and specialties but some concepts are relevant only to a particular environment. SNOMED CT is designed to allow the International Edition to be enhanced by adding Extensions to meet national or local requirements without compromising the main body of SNOMED CT. This is intended to meet the needs of different specialties and countries, regions, vendors and healthcare institutions.
Extensions are managed by IHTSDO Members or Affiliates who have been issued with a Namespace Identifier. A Namespace Identifier distinguishes the Identifiers of the Components created by an organization. The responsibilities of organizations that create an Extension and provide it for use by other organizations include:

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Software applications should allow the users or user communities to specify the Extensions to be recognized by their systems.
An Extension should only be recognized if:

• It has been supplied by the IHTSDO SNOMED International or another organization authorized by the IHTSDO SNOMED International to provide such Extensions;
• The recognizing organization is satisfied with the quality control procedures of the providing organization.

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