Ecole Polytechnique de

Free and open source software (FOSS) is distributed and made available to users under different software licenses, mentioned in FOSS code by means of licensing statements. Various factors, such as changes in the legal landscape, com-mercial code licensed as FOSS, or code reused from other FOSS systems, lead to evolution of licensing, which may affect the way a system or part of it can be subsequently used. Therefore, it is crucial to monitor licensing evolution. However, manually tracking the licensing evolution of thou-sands of files is a daunting task. After presenting several cases about the effects of licensing evolution, we argue that developers and system integrators must monitor licensing evolution and they need an automatic approach due of the sheer size of FOSS. We propose an approach to automati-cally track changes occurring in the licensing terms of a sys-tem and report an empirical study of the licensing evolution of six different FOSS systems. Results show that licensing underwent frequent and substantial changes