In the context of the EU FP7 project ''OSSMETER'' we are developing an infra-structure for measuring source code. The goal of OSSMETER is to obtain insight in the quality of open-source projects from all possible perspectives, including product, process and community. This is a "white paper" on M3, a set of code models, which should be easy to construct, easy to extend to include language specifics and easy to consume to produce metrics and other analyses. We solicit feedback on its usability.