Professor Stephen Lerman has been a leader in the field of mathematics education for thirty years. His work is extensive, making many significant contributions to a number of key areas of research. Stephen retired from South Bank University in 2012, where he had worked for over 20 years, though he continues to work at Loughborough University. In this book several of his long standing colleagues and collaborators reflect on his contribution to mathematics education, and in so doing illustrate how some of Steve's ideas and interventions have resulted in significant shifts in the domain.