Control Theory is an interdisciplinary field of engineering and mathematics that studies the behavior of dynamic systems with external stimuli and how to modify such behavior through feedback, and the very concept of dynamic system implies the study of how the trajectories of a point in a geometric space evolve in time. Thus, time is at the very foundation of control theory, and its development and achievements are conditioned both by the conception we have of it and by our way of measuring and using it. Following a quasi-chronological order, this work aims to give an overview of how these conceptions and these ways of measuring and using time are reflected in the paths followed by control theory from its origins to the present day.

Blas M. Vinagre Jara is a Telecommunications Engineer and a Doctor in Industrial Engineering. He worked as an R&D Engineer and Head of Department in various companies between 1985 and 1994, mainly in Electronic Warfare and Industrial Automation. In 1994 he became part of the current Department of Electrical, Electronic and Automation Engineering at the University of Extremadura, where he is currently a University Professor in the area of Systems Engineering and Automation. He is co-author of: 2 books, one of them published by Springer and a reference in Fractional Control (Concepción A Monje, YangQuan Chen, Blas M Vinagre, Dingyu Xue, Vicente Feliu-Batlle, Fractional-order Systems and Controls: Fundamentals and Applications, Springer 2010), 14 book chapters, around 50 articles in indexed journals, and more than 100 contributions to international conferences. He has organized or participated in the organization of various events, including the following: 4th IFAC Workshop on Fractional Differentiation and Its Applications (President of the organizing committee, Badajoz 2010), Tutorial Workshop on Fractional Order Control (IEEE CDC, Las Vegas 2002), Tutorial Workshop on Fractional Calculation Applied to Controls and Signal Processing (IEEE CDC, Atlanta 2010), Symposium on Fractional Derivatives and their Applications (ASME-IDETC 2007, 2009, 2011, 2013, 2015), XXXIX Conference on Automatics (Badajoz, September 5 to 7, 2018). He has been awarded the Honor Award at the 2nd IFAC Workshop on Fractional Differentiation and Its Applications (Porto 2006), and the Best Paper Award (Control Engineering Practice, IFAC World Congress, Milan 2011). He has been a member of numerous technical committees at international conferences, a reviewer for major automatic control journals, and is a reviewer for Mathematical Reviews. He is a member of the editorial board of Fractional Calculus & Applied Analysis, and has been associate editor of several special issues in indexed journals.He is a member of IEEE and IFAC, and a member of the IFAC Technical Committee on Linear Control Systems (TC 2.2). His research interests include stability theory, optimal, adaptive, and nonlinear control. He is currently a principal researcher in a national project whose objective is to develop biomimetic swimming robots at the millimeter and submillimeter scale, consolidating a new line of research by focusing his experience in control and robotics to biomedical engineering. His Google Scholar figures are: total citations: 14041; h-index: 46.

Introduction.- PID Control and the Sequence of the Time.- Control Theory, Time Concepts and Calculus.- Sampling and Integral Sums.- On Reversibility.- Feedback: Mixing Memory and Desire.- Fourfold Vision. A Code.