on a number of interrelated dimensions of DSL variability: variable development processes, variable design-decisions, and variability-implementation techniques for DSL. The three subsequent chapters are devoted to the key conceptual and technical contributions of DjDSL: Chapter 3 (¿Variable Language Models¿) explains how to design and implement the abstract syntax of a DSL in a variable manner. Chapter 4 (¿Variable Context Conditions¿) then provides the means to refine an abstract syntax (language model) by using composable context conditions (invariants). Next, Chapter 5 (¿Variable Textual Syntaxes¿) details solutions to implementing variable textual syntaxes for different types of DSL. In closing, Chapter 6 (¿A Story of a DSL Family¿) shows how to develop a mixed DSL in a step-by-step manner, demonstrating how the previously introduced techniques can be employed in an advanced example of developing a DSL family. The book is intended for readers interested in language-oriented as well as model-driven software development, including software-engineering researchers and advanced software developers alike. An understanding of software-engineering basics (architecture, design, implementation, testing) and software patterns is essential. Readers should especially be familiar with the basics of object- oriented modelling (UML, MOF, Ecore) and programming (e.g., Java).