The quality and success of a software product highly depends on its software architecture. Inappropriate decisions during the architectural design of a software system are often hard to reverse and might lead to costly and time-intensive changes later on. Therefore, software architects are required to make proper design decisions early on in the architectural design process. The goal of this thesis is the development of a recommender system for software architecture design decisions. The thesis starts by presenting basic concepts and terms of software architecture, software architecture decision making, and decision models. It then presents fundamentals of recommender systems including different kinds of recommender systems. The main part of the thesis is the presentation of the developed recommender system for software architecture decision making based on decision models. This includes a presentation of the main requirements of the system, of its conceptual realization, and of its implementation.