Maturing organizations rigorously define their software development processes in order to make them more predictable, investing a huge effort in this task. However, the same process may not be suitable for every project, since the most appropriate process depends on the execution context. Redefining the process for each project or just using the organizational process for all projects are both inadequate choices, so tailoring the general process according to particular project characteristics seems to be a good trade-off. But no systematic way of tailoring software processes has been established yet. In this paper we propose to use Model-Driven Engineering (MDE) techniques for rigorously defining the organizational and the project adapted processes as models, as well as the context, and the tailoring process as a model transformation. The transformation gets an organizational process model and a context model as input and it produces the project adapted process model.We illustrate the proposed approach with an example for a real world organization.