Quantum mechanics is one of the fundamental theories in physics and it deals with the elementary constituents of matter (atoms, subatomic and elementary particles) and of radiation. It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science. Entry Collection is created to collect entries and serve scholars better f-or their demands of information in relevant and latest studies. The academic editor of this Entry Collection is Prof. Marek Szopa, who works in University of Economics in Katowice. He has been researchi-ng on fields of quantum physics, quantum games and quantum communication for years.