We present the vision that for all fields of software engineering (SE), empirical research methods should enable the development of scientific knowledge about how useful different SE technologies are for different kinds of actors, performing different kinds of activities, on different kinds of systems. It is part of the vision that such scientific knowledge will guide the development of new SE technology and is a major input to important SE decisions in industry. Major challenges to the pursuit of this vision are: more SE research should be based on the use of empirical methods; the quality, including relevance, of the studies using such methods should be increased; there should be more and better synthesis of empirical evidence; and more theories should be built and tested. Means to meet these challenges include (1) increased competence regarding how to apply and combine alternative empirical methods, (2) tighter links between academia and industry, (3) the development of common research agendas with a focus on empirical methods, and (4) more resources for empirical research.