This book contains the proceedings of the Gregory Breit Centennial Symposium. The legacy of Breit to atomic, nuclear and particle physics is discussed vis-à-vis modern developments in these fields. Among other subjects, the present status of the Breit interaction in atomic physics and of the nucleon-nucleon interaction are reviewed. The second part of the book contains a more in-depth presentation of the status of modern nuclear physics, from relativistic heavy ion physics to nuclear structure physics and nuclear astrophysics. The recently confirmed discovery of supersymmetry in nuclei...