Evidence (in different forms) is widely employed to establish and refine ideas about what constitutes good practice in many domains of science and engineering. However, Software Engineering (and computing in general) has so far been a notable exception to this, and our paper sets out to explore some of the reasons why this should be so, and how the situation might be changed in the future. We examine the ways in which some other domains collect and use evidence, and then examine both 'commercial' and 'open source' developmentpractices to see how these currently make use of previous experience and evidence. Finally, we consider the possible role of systematic review groups in strengthening the way that evidence could be employed in future Software Engineering practices.