The interviewer session engine (mrIEng.dll) controls the creation of new interviews (see Starting inbound interviews and Starting outbound interviews) and acts as an interface between the components of the Interview Service, as shown in the following illustration:

When a site has more than one Interviewing server or a single server running more than one interviewer session engine, the load balancing system ensures that interviews are evenly distributed across the available engines. See Load balancing interviewing engines for more information.