Metamagnetism and the Possibility of Novel Phase Formation Andrew P. Mackenzie School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland In this talk I will present a summary of recent research on the phase diagram of the itinerant metamagnet Sr3 Ru2 O7 , showing that crystal purity is crucial in revealing a wealth of new and unexpected physics. The results that I will discuss are collaborative, involving input from groups in Birmingham, Cambridge, Dresden, Kyoto and Tokyo as well as St. Andrews. Sorting category: Cb Magnetism and properties of solids Keywords: metamagnetism, strongly correlated electrons, ruthenates, quantum criticality INVITED PAPER LT1968