Programming languages have a dual role in the construction of software. The language is both our substrate (the stuff we make software from), and our tool (what we use to construct software). Program transformation (PT) deals with the analysis, manipulation and generation of software. Therefore a close relationship exists between program transformation and programming languages, to the point where the PT field has produced many domain-specific languages for manipulating programs. In this article, I will show you some interesting aspects from one of these languages : Stratego.