Use of Open Source Software (OSS) projects is increasing in the corporate environment, thereby creating a need for an evaluation framework for these projects. Owing to the significant differences in the development process of open source from the traditional software development model, the Capability Maturity Model framework cannot be directly applied to the OSS development environment. For organizations evaluating OSS for adoption, a framework that provides a barometer of process maturity in the open source development environment can be valuable. To this end, we propose a framework of Open Source Maturity Model and describe the key process areas for different levels of maturity as relevant to OSS domain.