William Simpson is a postdoctoral fellow at The Weizmann Institute, Israel. He completed his PhD at the University of St Andrews in 2014, having graduated with a first class MPhys in Theoretical Physics and Mathematics in 2010 and been awarded a SUPA Prize Doctoral Studentship. During the course of his research on Casimir forces, William was a visiting student at the University of Trento and The Weizmann Institute. He also founded a Physics & Philosophy Society (PhysPhil), and was the chief organiser of St Andrews' first two Philosophy of Physics conferences and the Foundations of Casimir Physics symposium in Stockholm.

• Part I Foundations of Casimir Theory.- Casimir's Calculation.- Macroscopic Quantum Electrodynamics.- The Quantum Nature of the Casimir Force.- Part II Surprises in Casimir Theory.- The Cut-off-dependence of the Casimir Force.- The Divergence of the Casimir Stress.- Part III Conundrums in Casimir Theory.- The Casimir Force in a `Compressive' Medium.- The Casimir Force in Maxwell's Fish-Eye.- Outlook.- Appendices.