This book aims to describe the physics of the integer and fractional quantum Hall effects (QHE) from a theoretical side. In the classical Hall effect, the Hall resistance is proportional to the applied magnetic field strength and varies continuously. So, the discovery of a stepwise change of the Hall resistance by von Klitzing in an ultra-thin layer of a MOSFET was a big surprise. The QHE is a macroscopic phenomenon and shows the exact quantum structure, which is one of the most fundamental phenomena in physics. The fractional quantum Hall effect has been explained assuming quasi-particles with fractional charges or Jain's composite fermions, the existence of which has not been verified experimentally. The author has been developing a theory based on a standard treatment of an interacting electron system without assuming any quasi-particle. This book will be easily understood by undergraduate students in physics. Knowledge of quantum field theory is needed to study Chapter 9.

Bose-Einstein condensation was discovered in atomic gas systems, where Bose condensate occupies 100% of the total system at zero temperature. Liquid helium systems have been investigated based on the Landau theory, where the superfluid component of liquid helium is background flow. According to the Landau theory, it is doubtful that the superfluid component is a Bose condensate. In experiments, the probability of helium atoms with zero momentum is a few percent of the total liquid helium at ultra-low temperatures. However, the superfluid component occupies 100% of the liquid helium at zero temperature, as macroscopic observations indicate. This new book introduces a quasi-particle representing an eigenstate of the total Hamiltonian