Software Processes and Software Process Modeling approaches were and still are in the heart of enterprise preoccupations. This interest is essentially motivated by the increasing need to build reliable and complex software systems in a short time to market. During the three last decades, a variety of Process Modeling Languages were proposed in order to capture the expertise of enterprises. However no one succeeded in gaining the attention of the industry. Main reasons were because that most of them were either imprecise or not suitable to be executed or both. This paper presents UML4SPM, a UML2.0-based Language for Software Process Modelling. Expressiveness, understandability, precision and executability were our main objectives while designing UML4SPM. Our contribution comes in form of MOF-Compliant metamodel, a simple yet expressive graphical notation and diagrams and a precise semantics. In order to validate our work, we evaluate UML4SPM with the well-known ISPW-6 process example, a standard benchmark problem for software process modeling.