Chemical batch plants and their sequential control systems are regarded as discrete event systems. There has recently been great interest in the control of these systems. This paper first formulates a control problem for discrete event systems as follows: given the controlled plant modeled by a condition/event net (C/E net) and some specification of the desired behavior described by a partial language, synthesize a controller to realize the specified behavior. It next studies the properties of this C/E net control problem and then presents a method of finding solutions. It also discusses the practical applications of the control problem to the design of sequential control systems.