Abstract. The most popular Software Process Models worldwide are ISO/IEC 15504 and CMMI. It is desirable for organizations to have assessments according to both these models but every assessment is expensive both financially and time-wise, and furthermore new assessments are required when a new models version is released. In order to define and/or to improve their software process, organizations choose different Software Development Methodologies. It is important for the organization to know what capability/maturity of the process a chosen methodology could ensure. In order to solve these problems we propose Transitional Software Process Model (TSPM). It enables the transformation of results of an assessment according to one Process Model to other models and determines what capability/maturity according to different Process Models a chosen methodology could ensure. Also, TSPM ensures transition of the existing assessment results to a new version of the model without reassessment. The principles of TSPM implementation are given in this article.