What is the difference between ISDN and SS7?

The Integrated Services Digital Network (ISDN) uses Digital Subscriber Signalling System No. 1 (DSS1) protocol interfaces to connect subscribers to the network. These are User-to-Network (UNI) interfaces.

Signalling System No. 7 (SS7) is a suite of signalling protocols used in Network-to-Network (NNI) interfaces. These are connections between network elements within the ISDN.