This paper proposes an integration of the situation calculus with justification logic. Justification logic can be seen as a refinement of a modal logic of knowledge and belief to one in which knowledge not only is something that holds in all possible worlds, but also is justified. The work is an extension of that of Scherl and Levesque’s integration of the situation calculus with a modal logic of knowledge. We show that the solution developed here retains all of the desirable properties of the earlier solution while incorporating the enhanced expressibility of having justifications.