Recent electricity price spikes are painful reminders of the value that meaningful demandside responses could bring to the restructuring US electricity system. Review of the aggregate offers made by suppliers confirms that even a modest increase demand elasticity could dramatically reduce these extremes in price volatility. We submit that dramatically increased customer participation in these markets to enhance system reliability and reduce price volatility is sorely needed. Indeed, allowing customers to manage their loads in response to system conditions might be thought of as the ultimate reliability resource. Most would agree that meaningful demand-side responses to price are the hallmark of a well-functioning competitive market (Kirby and Kueck 1999). Yet, in today's markets for electricity, little or no such response is evident. In effect, today's markets are incomplete; they represent only half of what a truly competitive market requires. The reason is simple: customers currently do not experience directly the time-varying costs of their consumption decisions. Consequently, they have no incentive to modify these decisions in ways that might enhance system reliability or improve the efficiency of the markets in which electricity is traded. We submit that increased customer participation is a necessary step in the evolution toward more efficient markets for electricity and ancillary services. Toward this end, this paper outlines an agenda for public-interest R&D in support of this objective.