This paper describes a mechanism to enable users of performance modeling tools to transfer models among a set of tools. This paper describes the evolution and definition of a basic PMIF. It describes how tool developers can implement the PMIF and how the export and import would work for users. A simple example illustrates the format. The paper describes how to extend the PMIF to add new features to the basic format. It ends with the current status of the PMIF, what we have learned, some suggestions for sets of extensions, and current work in progress