My name is Christian Rehn and I'm a software developer from Germany. When I started programming in 2001, naturally my first design choices were extremely bad. And I had no idea that this was the case. When I finally realized that my complete lack of experience resulted in unmaintainable and fragile designs, I wondered how to distinguish good design choices from bad ones. Over the time I found out that there are many design principles or rules of thumb which help making good design decisions. In 2012/2013 I wrote my Master's thesis about these principles. The notion principle language and also this wiki were created in the course of the thesis. Since then I slowly but steadily continue working on the topic and the wiki.