With a rapid technological change and an increasing number of health technologies emerging in contrast to scarcity of the resources, the decision-makers in the health care sector face a dilemma. This has highlighted the importance of health technology assessment, which as a form of policy research provides input to decision-making in policy and practice. Written as a Ph.D. thesis, this book presents various important aspects of health technology assessment (HTA). A broad range of publications concerning theory and methodology in the area of HTA has been reviewed and empirical studies of HTA and diffusion have been conducted. The empirical studies covered in the book are an international comparison of health technology assessment including Sweden, the Netherlands, the United Kingdom, Canada and Australia, as well as empirical studies of the diffusion of laparoscopic technologies in Denmark and the Netherlands.