Jonathan Pila is Reader in Mathematical Logic and Professor of Mathematics at the University of Oxford, and a Fellow of the Royal Society. He has held posts at Columbia University, McGill University, and the University of Bristol, as well as visiting positions at the Institute for Advanced Study, Princeton. His work has been recognized by a number of honours and he has been awarded a Clay Research Award, a London Mathematical Society Senior Whitehead Prize, and shared the Karp Prize of the Association for Symbolic Logic. This book is based on the Weyl Lectures delivered at the Institute for Advanced Study in Princeton in 2018.