A collection of papers on statistical mechanics which elucidate Bogolubov's microscopic theory of superfluidity and reflect his contribution to the explanation of superconductivity. This book also shows the inception of the concept of quasi-averages, containing the idea of spontaneous symmetry breaking, which was to have a significant influence in elementary particle physics and quantum field theory. This volume offers insight into the fundamental concepts that underpin aspects of modern physics, from the theory of electromagnetic and weak interactions to phase transitions. It is directed at undergraduates exploring statistical mechanics and at graduates and researchers developing Bogolubov's fundamental results.