Ken Riley is a retired Lecturer in Physics at the University of Cambridge Cavendish Laboratory. He is also a Fellow of Clare College, Cambridge, where he was both the Senior Tutor and Admissions Tutor, and taught physics and mathematics for over forty-five years. He has served on many committees and panels concerned with the teaching and examining of these subjects at all levels of tertiary and university education. His research was centred on nuclear physics at Harwell and then elementary particle physics at Brookhaven, New York, the Rutherford Laboratory and Stanford. He is the lead author of Mathematical Methods for Physics and Engineering (Cambridge, 3rd edition, 2006), and a joint author of both Foundation Mathematics for the Physical Sciences (Cambridge, 2011) and Essential Mathematical Methods for the Physical Sciences (Cambridge, 2011). He is a co-author of 200 Puzzling Physics Problems (Cambridge, 2001) and the consultant editor for 200 More Puzzling Physics Problems (Cambridge, 2016).