Demand for electricity continues to grow in the U.S. By some estimates, the demand is expected to increase as much as 40% by the year 2030. Traditional approaches to meet the demand would require significant resources. However, part of the growth can be offset by making the grid “smart” through increased availability of energy-information technologies. Making the grid smart is only half the solution. The other half of the solution is to make the buildings “smart” as well. Because buildings consume over 70% of the total electricity in the U.S., they need to be part of the transformation to make the grid smarter. However, many commercial buildings and almost all residential buildings lack proper infrastructure to be part of such a transformation. The evolving smart electric utility grid will further increase demands on building systems to automatically respond to time-varying prices and conditions on the grid as the grid is operated at shrinking reliability margins and relies on demand response to manage loads. Smart building systems will be essential for meeting these needs. In this paper, we describe market-based transactive controls that can be implemented in an existing building automation system (BAS) with little or no additional capital expenditure to make commercial buildings more demand responsive. Although this paper only shows the application of market-based transactive controls to commercial building with BASs, the concept can be applied to any thermostatically controlled devices with one- or two-way communication. We also describe a case study that qualitatively shows the value of the market-based controls.