Summary: GrGen.NET is a generative programming system for graph rewriting, transforming intuitive and expressive rewrite rule specifications into highly efficient .NET code. The user is supported by a convenient environment consisting of a graph viewer, an interactive shell with integrated debugging support, and an elegant domain-specific language for the combination of rewrite rules. After rapid prototyping with these tools, the resulting graph transformation programmes can be easily integrated into arbitrary .NET applications to serve as the algorithmic kernel. Expressiveness, convenience, and speed are exemplified by GrGen-solutions to the case studies AntWorld, Refactoring, and Conference Scheduling-besides others.