The talk concerns the recent work with Baltieri, Biehl and Virgo on a categorical account of the classical 'internal model principle' from control theory and cybernetics in a broader sense. The aim is to distill the mathematical content of such an informal principle, following previous work of Wonham and Hepburn. In the talk I only use elementary mathematical notions and thus should be accessible to an audience acquainted with the basic vocabulary of sets and dynamical systems.