Contrary to what its title suggests, this book - Quantum Mechanics II - is not a continuation of Quantum Mechanics but a separate book for teaching quantum theory at a more advanced - yet still undergraduate - level. It is, therefore, Quantum Mechanics Level II as opposed to Quantum Mechanics Level I, which is already available. Like Quantum Mechanics I, Quantum Mechanics II has a strong interdisciplinary focus. One of its main goals is to encourage the "meeting" of physicists, mathematicians, and computer scientists in the emerging common field of quantum computing and quantum information. The organization and presentation of the material have been particularly carefully considered so that the book is equally accessible to all its reader groups. An entire section of it - "Approximate Methods" - is also externally marked to make it clear that it is mainly intended for physicists, while it is advisable to omit it in a course for mathematicians and computer scientists.