Design encompasses some of the highest cognitive abilities of human beings, including creativity, synthesis and problem solving. A substantial and varied range of research methods has been developed and adopted for the analysis of design activity, but until now it has been difficult to compare the work of different researchers using different methods. This book contains the results of an international workshop held in Delft, The Netherlands, which focused on one particular research method, that of protocol analysis. Researchers from seventeen different leading centres around the world were invited to analyse the same video recordings of designers working on an engineering product design. The 20 chapters in this book are the records of that workshop, providing rich insights into the design process and an overview of accumulated knowledge on design from these researchers. There is also a discussion of the properties and limitations of protocol analysis as a research technique for analysing design activity. The book is a substantial contribution to developing understanding of the nature of design activity, and is of value to researchers, teachers and practitioners of design.