Discussing changes over the last two decades, including the expanded number of available experimental systems and potential applications, this book represents the most complete and up-to-date treatment of superfluidity. It covers new superfluid materials such as high-temperature superconductors, ultra-cold atomic bosons and fermions, and helium supersolids. The text begins by explaining the general physical principles behind the superfluid phenomenon as a framework for the discussion of realistic systems. The authors present superfluidity as a phenomenon of emergent topological order and show that all superproperties of the system are explained by the appearance of a new constant of motion.