How is a service delivered between departments of the same organization classified?

An internal service is one delivered between departments or business units that belong to the same organization, as opposed to being delivered to an external customer. ITIL distinguishes internal from external services because this relationship affects how service levels, agreements, and funding models are structured. Recognizing this classification helps organizations apply appropriate governance to intra-organizational service delivery.

An external service is delivered to customers or parties outside the service provider's own organization, not between internal departments.

Mission critical service describes the relative importance or business impact of a service, not the relationship between the service provider and consumer.

'Organizational service' is not a standard ITIL service classification used to define internal versus external delivery relationships.