Over the last decade, the explicit introduction and management of variability in the development cycle of (software) systems has led to a plethora of modelling and analysis techniques tailored to deal with such highly configurable (variational) systems. Most of the work on Variability Modelling and Analysis, however, focusses on qualitative (i.e. functional) requirements. This Special Section of the Foundations for Mastering Change track of the International Journal on Software Tools for Technology Transfer on Quantitative Variability Modelling and Analysis aims to provide a comprehensive overview of the latest approaches to Variability Modelling and Analysis techniques which specifically take quantities into account. In this paper, we first introduce Quantitative Variability Modelling and Analysis, after which we briefly describe the contents of the six papers that constitute this Special Section.