Abstract. In this paper, the mobility of software processes, a novel concept, is proposed. It is defined as the structural change in a software process resulting from interactions among linked process elements. The concept addresses the essential change in a software process which brings a high variability and unpredictability to process performance. Three categories of mobility that lead to the structural change are identified and expounded upon. A reference model for describing the concept is put forward on the base of polyadic π-calculus. With the mobility of software processes, it is possible to design a new PCSEE and associated PML with reduced inconsistencies between process enactment and process performance.