In the past century, during my studies in electronic engineering at the Politecnico di Milano, I had two courses in control science, a course called automatic control in my fourth year and, in the fifth year, a course on regulation theory. It was during the lectures of this last course that I had the chance to come into contact with the new world of system ideas for control, such as state-space representation, canonical decomposition, and so on. I found these concepts very appealing, so much so that I embarked on a master's thesis on controllability and observability. It was during these studies that I became aware of the work of Rudy Kalman. © 1991-2012 IEEE.