A discussion of fundamental problems in quantum physics, with emphasis on quantum coherence and decoherence. Papers covering the wide range of quantum physics are included: atom optics, quantum optics, quantum computing, quantum information, cryptography, macroscopic quantum phenomena, mesoscopic physics, physics of precise measurements, and fundamental problems in quantum physics. The text should serve not only as an introduction to quantum coherence and decoherence for newcomers in this field, but also as a reference for experts.