The authors, from their position as independent consultants and designers of building management systems (EMS), discuss their experiences in the design of direct digital control (DDC) based systems. The performance design of distributed processor DDC-BMS is outlined for a number of major projects including a university, 38 Federal government buildings, a health sciences complex and a large commercial Office/retail development. Comment is provided upon the primary advantages of DDC over the more conventional control point adjust techniques and the salient design features of DDC-EMS are identified. Opinion is expressed as to potential future trends in the development of BMS.