: In this paper I explain the benefits of projectional language workbenches for product line engineering. The ability to extend programming languages with domain specific concepts, mix programs (i.e. descriptions written in general purpose languages) and models (i.e. descriptions expressed with DSLs) and also overlay configurative variability to both of these promises highly integrated and productive tools for product line development. 1 Variability in PLE In the context of product line engineering, DSLs are used to bind variability. We distinguish between two kinds of variability: structural and non-structural. Structural variability is described using creative construction DSLs, whereas non-structural variability can be described using configuration languages. Figure 1 illustrates the spectrum of languages commonly used for expressing and binding variability, reusing an illustration from Krzysztof Czarnecki. Figure 1 Spectrum of Variability Let's look at two well-known ways of r...