Dutra (British Institute of Physics) addresses the question of what happens to light when it is trapped inside a box. With the aid of a model-building approach, readers discover the answer to this question and come to appreciate its important applications in computing, cryptography, quantum teleportation, and opto-electronics. Instead of requiring readers to first master a series of seemingly unconnected mathematical techniques, the book engages the imagination and introduces mathematics along the way as needed. Appendices explain additional mathematical theory. The book can be used in an advanced undergraduate quantum mechanics course.