Chapter | 17 Demand Response Participation 425 Response Participation in the Capacity Market" describes DR participation in the RPM Capacity Market with a brief history of DR participation as a capacity resource prior to RPM. Section "DR Participation in the Energy Market (Day- Ahead and Real-Time)" provides a short history of DR participation in PJM's Energy Markets and describes the mechanisms by which DR currently participates in PJM's Day-Ahead and Real-Time Energy Markets. Section "DR Participation in Ancillary Service Markets" summarizes DR participation in Ancillary Service Markets. Section "Administration of DR in PJM's Markets" briefly outlines how PJM administers DR participation in its markets, and section "DR Participa- tion Going Forward: Current Issues related to Demand Response" concludes with an examination of current and emerging issues facing DR participation in PJM's markets. ENTITIES THAT PARTICIPATE AS DR IN PJM'S MARKETS When one thinks of demand response (DR), it is natural to envision the end-use customer, whether it is a household a commercial customer, or an industrial customer that is engaged in reducing energy usage. However, these customers (with a few exceptions) are taking electricity service at the retail level and PJM operates at the wholesale level. Consequently, there needs to be a third party