Abstract. Software tool integration and integrated environments for software project development, i.e., integrated computer aided software engineering (CASE), have become important mechanisms for producing software in an effective and efficient manner. This article is not a presentation of another such environment or a description of another technique for integration. Rather, it presents a categorization of degrees of tool integration and integrability. It is useful to identify the level of integration or integrability before any problems caused by an inappropriate level of integration can be overcome. This categorization is qualified by three parameters: granularity, coherence, and harmony. These parameters can be applied to each component of a typical programming environment, i.e., to a project information base, software development tools, and user interface. Combinations of values of these parameters form a continuum of levels of integration from loose to tight. This research was motivated by the need to understand the levels of integration that are possible and the characteristics that facilitate such integration in order to evaluate the level of integration of tools sets and to more effectively integrate new and existing tools into productive environments. The article closes with an application of these parameters to some existing software environments and sets of tools.