Recent technological advances have made it possible to perform experiments, once considered to be purely gedanken, which test the counterintuitive and bizarre consequences of quantum theory. This book provides simple accounts of these experiments and an understanding of what they aim to prove and why this is important. After introducing the main theoretical concepts and problems with the foundations of quantum mechanics, early chapters discuss experiments in the areas of wave-particle duality, cavity quantum electrodynamics and quantum nondemolition measurement. The text then examines investigation of new predictions, including the Aharanov-Bohm effect, before tackling the problem of macroscopic quantum coherence. Later chapters consider methods of testing the quantum Zeno paradox, collapse, macroscopic quantum jumps, tunneling times and Einstein-Bell nonlocality. Introductions to the theory behind new types of measuring devices such as micromasers and those based on the concept of quantum nondemolition are also given. Detailed references are included.