Causal operators acting, by definition, on the past and present functions of time are first presented. Then are described dynamic systems involving a causal operator in their evolution equation, both in the cases of a continuous and a discrete time. A first example of causal dynamic system is given by the modelling of a subject observing an object (Von Forster 1976). The operator involved acts in fact only on the present. In case of convergence it gives rise to an “eigen-behavior” representing the stabilized state of what concerns the modes of action of the subject and of what concerns the object. Then is presented the concept of “epistemo-praxiology” (Vallee, 1974, 1995) involving an “observation operator” (Vallee, 1951), then decision and effect operators. All these operators are causal (acting upon past and present). They explain the subjective limitations of the observing and deciding subject in front of an object (pragmatic indiscursibility and pragmatic inverse transfer of decisional structures). They show also the coevolution of the subject and the object as a fixed point of a composite operator having observation, decision and effection traits. The notions of “incursivity” and “hyperincursivity” (Dubois and Resconi, 1992; Dubois, 1995) involve operators acting on the past, present and future of functions of time and considerations linked to Aristotle’s final causes. They give tools for solving problems of stability of certain systems.