This book contains the proceedings of the Gregory Breit Centennial Symposium. The legacy of Breit to atomic, nuclear and particle physics is discussed vis-a-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 is also discussed.