||In the world of designing, three fields of attention can be recognised, namely design research, design practice, and design education. Gaps exist between these three fields. In this thesis about designing, the focus is on the gap between design research and design practice. Design practice includes many design disciplines and an increasing number of multidisciplinary teams. Main problems in design practice are the communication between designers with a different background and the integration and co-ordination of important aspects during a design process. By tackling these problems, the effectiveness and efficiency of design processes in practice can be improved. The study of similarities and differences between design processes in several design disciplines and the development of support for reflection on design processes are topics that can improve design practice and that deserve more attention in design research. The goal of my research is to decrease the gap between design research and design practice in order to improve design processes. Reflection on design processes can help designers to improve their design process, its results, and the designer’s proficiency: By reflecting explicitly on the current design situation and on the performed design activities, in a systematic way and on a regular basis, designers can plan next design activities that can be performed effectively and efficiently given the design goal at that moment. In this thesis, the combination of systematic and regular reflection is called structured reflection. To improve design processes in various design disciplines in practice, the study of similarities and differences between design processes in several disciplines can be useful. Similarities between design processes are the basis for domain-independent design knowledge (as distinguished from domain-specific design knowledge). To reach the goal of my research, I have chosen to combine, in a broad explorative study, the development of support for structured reflection on design processes and the development of domain-independent design knowledge. This thesis describes a domain-independent approach to improve design processes through structured reflection. My research process can be summarised as follows. I studied three design disciplines, namely architecture, mechanical engineering, and software engineering. To get input from design practice, I did qualitative empirical research: I performed twelve case studies in the three disciplines to inventory characteristics of design processes and I compared the cases for similarities and differences. The similarities, together with the results of a literature study, have been the basis for the development of domain-independent descriptive design knowledge. The developed descriptive knowledge, in turn, formed the basis for developing domain-independent prescriptive design knowledge. At the end of the project, I confronted all results with design practice to get feedback on the results in another empirical study and I performed a literature study to position the results in the design literature. My design philosophy and design frame are the descriptive results developed to answer the first research question, namely “How to describe design processes in a domain-independent way?”. My design philosophy is a set of domain-independent concepts and terms for describing a design process. The concepts and terms are based on an application of the general theory of state-transition systems to the context of designing; the concepts of state and state transition correspond to the main concepts of design situation and design activity in my design philosophy. The answer to the first research question given by the design philosophy is refined in a design frame: The design frame offers a means to structure the description of a design process in a domain-independent way. Major structuring concepts of the design frame are dimensions and subjects. I define three dimensions, namely level, perspective, and time. These dimensions define a three-dimensional space, called a positioning space, in which important aspects of design processes can be positioned. A positioning space must be defined for each subject, being the three parts of a design situation: the product being designed, the design process, and the design context. My design frame is a domain-independent structure formed by the combination of the three dimensions for each subject. My design method is the prescriptive result developed to answer the second research question, namely “How to support structured reflection on design processes in a domain-independent way?”. My design method is a domain-independent aid that offers designers support for reflecting on design processes in a structured way. Reflection on design processes is defined as an introspective contemplation on the designer’s perception of the design situation and on the remembered design activities. A reflection process is described as a process that consists of three steps that are called preparation, image forming, and conclusion drawing. The design method is based on two main concepts: The first concept is the systematic description and analysis of design situations and design activities by means of forms and checklists; only systematic support for the preparation step of a reflection process is developed. The second concept is the idea of design sessions, introduced to stimulate designers to reflect regularly during a design process. A design session is defined as a period of time during which one or more designers are working on a subtask of a certain design task, for example, one afternoon, a whole day, or a week. Both concepts are combined to support structured reflection on design processes. The complete design method consists of five steps for each design session, namely planning a design session, defining the subtask of the design session, reflecting at the beginning of a design session, designing during the core of a design session, and reflecting at the end of a design session. A prototype software tool, called ECHO, has been developed to explore the benefits of using a software system to facilitate the use of the design method. Together, the design philosophy and the design frame offer concepts, a vocabulary, and a structure to describe design processes in a domain-independent way. The design method is a first proposal of a method that supports structured reflection on design processes. My results are thus possible answers to the mentioned research questions and are starting points to improve the effectiveness and efficiency of design processes. Based on the feedback I collected, I am optimistic about the applicability of my results in design practice. By asking input from design practice and by developing results that are useful for design practice and that contribute to design research, I contribute to decrease the gap between design research and design practice. The most important recommendations for further research are to test all results extensively in design practice and to investigate how to apply the results in design education.