This is the fifth in an integrated group that deal with the stability and response of linear systems. ESDU 80018 deals with the function of the different system elements and with design techniques used to construct a system with the required characteristics. Proceeding from the essential first step of the definition, in a mathematical form, of the plant to be controlled, it considers the means by which the control of the plant may be enhanced by the application and limitation of different control elements. Once the control strategy has been chosen consideration is given to the changes that are necessary within the system to achieve the required performance. The conclusion discusses the overall effects and consequences of the successful control policy.