This dissertation describes a methodology for assessing the software process (both development and maintenance) used by an organization. The assessment methodology integrates the principles of Total Quality Management and the work of the Software Engineering Institute. The integrated assessment methodology results in a well understood, well-documented, quantitatively evaluated software process. The methodology utilizes four steps: investigation, modeling, data collection, and analysis of both process content and process output. The integrated assessment methodology was implemented at a large commercial software organization over a two year period. Implementation results are presented and significant conclusions are discussed. Four areas for further research are also presented. / Ph. D.