: Numerous design decisions are made in model-driven software development which are mostly implicit and not documented properly. Hence, the design knowledge is usually 'in the designers mind' and maybe propagated orally, if at all. There exist tools which tackle that problem for architectural decisions which refer to the higher level architecture of the system to develop, but these decisions are not linked to the design models and are only for documentation. The goal of this project is to contribute concepts and a tool for explicit design decision support in model-driven software development. The contribution is twofold: a technology for creating and storing model differences is developed which will be used for storing model changes for reusable decisions; furthermore, an integration of decision management tools with modeling tools is presented. This allows explicit decision making with tool support and decision reuse which improves the design documentation process and allows...