The Service Catalog is the primary means through which the IT organization makes services known to customers and users.  The services in the catalog are a subset of those in the IT Portfolio, since the IT Portfolio identifies all services, including those envisioned, in development, operational, and retired, whereas the Service Catalog lists services that are in development and operational. 

There may be multiple views of the Service Catalog for different users.  Typically, an IT organization has both a strategic Service Catalog and a tactical Service Catalog.  The strategic Service Catalog lists high-level IT services that are used to establish Service Level Agreements between the IT organization and IT Customers.  The strategic Service Catalog is used by Service Level Management for IT customers.

In contrast, the tactical Service Catalog lists lower-level IT services that can be requested by users, such as access requests, asset moves or reassignments, desktop/laptop software installation, minor change requests, etc.  These low-level services are provided to users often because of SLAs enacted via the strategic Service Catalog.  Requests from the tactical Service Catalog often are processed by the Request Fulfillment process.