Invoking (or calling) is a means for one piece of code to let another piece of code to perform some operation. In a Service Oriented Architecture, invocations are usually performed over a network. In some cases, the two services may exist on the same physical machine or VM and there is no need to travel the network.

Invocation usually involves a client calling some interfaces operation. This triggers a client-side stub to serialize the call and the parameters and move them across the network to the provider where the operation is carried out.