A process logic (PL) is defined that subsumes Pratt's process logic, Parikh's SOAPL, Nishimura's process logic, and Pnueli's Temporal Logic in expressiveness. The language of PL is an extension of the language of Propositional Dynamic Logic (PDL). A deductive system for PL is given which includes the Segerberg axioms for PDL and it is proved that it is complete. It is also shown that PL is decidable. © 1982.