Control systems are essential ingredients of automation systems in a multitude of technology domains. By exploiting systems theory a language is developed to handle systems described by differential equations irrespective of the domain of origin. This enables the analysis and synthesis of interconnections of e.g. electrical, mechanical, thermal and chemical systems into one setting. The principle of feedback is ubiquitous in nature and in engineering. Feedback control is studied and feedback control design methods are developed that guarantee stability and high-performance of the resulting systems.