This ICB Research Report constitutes the proceedings of the Third International Workshop on Variability Modelling of Software-intensive Systems (VaMoS'09), which was held from January 28-30, 2009 at the University of Sevilla, Spain.

This ICB Research Report constitutes the Proceedings of the 4th International Workshop on Variability Modelling of Software-intensive Systems (VaMoS'10), which was held from January 27-29, 2010 at the Johannes Kepler University Linz.