Isospin Symmetry Breaking in Hadrons and Nuclei
  A brief review of the isospin symmetry breaking in hadrons and nuclei is given with emphasis on the $u-d$ quark mass difference. The off-shell $\rho^0-\omega$ mixing is studied as a typical example of the symmetry breaking, and its relevance to the nuclear force and nuclei is discussed. 
Tetsuo Hatsuda