Abstract A process concept is introduced similar to that of Staples and Nguyen ( Theoret. Comp. Sci. 26 (1983), 343–353), but more general. Processes are represented by the sets of scenarios they areable to realize. They communicate via shared places. A partial order of processess and some operations of combining processes similar to those of Milner (Lecture Notes in Comp. Sci. 93 (1980)) are defined. The partially ordered set of processes is a complete lattice. The operations preserve least upper bounds.