Abstract. A new equational foundation is presented for the Fluent Calculus, an established predicate calculus formalism for reasoning about actions. We discuss limitations of the existing axiomatizations of both equality of states and what it means for a uent to hold in a state. Our new and conceptually even simpler theory is shown to overcome the restrictions of the existing approach. We prove that the correctness of the Fluent Calculus as a solution to the Frame Problem still holds under the new foundation. Furthermore, we extend our theory by an induction axiom needed for reasoning about integer-valued resources. Stream: Knowledge Representation and Non-monotonic Reasoning