Collection of objects that actually do most of the work in WF. There are some required services that are always present, if the developer add one that is used otherwise a default is used. For example the DefaultWorkflowSchedulerService is the default implementation of the rquired WorkflowSchedulerService. Some other RuntimeServices are optional but provided out of the box like the SqlWorkflowPersistenceService. If not provided there is no default and this functionality is unavailable. The third kind of RuntimeServices is the custom RuntimeServices usually developed in combination with a custom workflow Activity. These services can use the WorkflowRuntimeService as a base class although this is not required and they can derive from another class is so desired. Use the WorkflowRuntime AddService function to configure the WorkflowRuntime.