A runtime engine of WF provides the basic functionality to EXECUTE and manage the workflow lifetime. It runs within the host process and is RESPONSIBLE for executing each workflow instance. A host process can interact with multiple runtime engines at a time, where each engine executes multiple workflow instances.

The host process interacts with runtime engine by using any of the following classes:

1. WorkflowInvoker : Invokes a workflow as its method.
2. WorkflowApplication: Controls the execution of a single workflow instance EXPLICITLY.
3. WorkflowServiceHost: Hosts the workflows and ALLOWS sending and receiving messages among VARIOUS instances of workflows.

A runtime engine of WF provides the basic functionality to execute and manage the workflow lifetime. It runs within the host process and is responsible for executing each workflow instance. A host process can interact with multiple runtime engines at a time, where each engine executes multiple workflow instances.

The host process interacts with runtime engine by using any of the following classes: