We present a hybrid discrete-continuous extension of Reiter's temporal situation calculus, directly inspired by hybrid systems in control theory. While keeping to the foundations of Reiter's approach, we extend it by adding a time argument to all fluents that represent continuous change. Thereby, we ensure that change can happen not only because of actions, but also due to the passage of time. We present a systematic methodology to derive, from simple premises, a new group of axioms which specify how continuous fluents change over time within a situation. We study regression for our new hybrid action theories and demonstrate what reasoning problems can be solved. Finally, we show that our hybrid theories indeed capture hybrid automata. </p