A remarkable achievement in theoretical physics has been the development of powerful many body techniques capable
of quantitative description of important phenomena. I shall not speak here about the technical aspects of these calculations, nor about the elegant field-theoretical techniques (Feynman graphs); I shall rather concentrate on qualitative interpretation of several interesting situations.

1. Choice of relevant degrees of freedom. A beautiful example is the coexistence of collective and single-particle degrees of freedom. In nuclear physics these are the rotation (vibration) and single-nucleon motion. In hadron physics we have chiral dynamics (mesonic field) interacting with quarks (analogously as phonons interacting with polarons).

2. Fine tuning of natural constants. If masses of elementary particles and interactions between them were slightly different,
life would not be possible. Many body effects often enhance such features. I shall present many picturesque examples.

3. Comparison of the shell structure in atoms, nuclei hadrons. Are three "generations" of quarks and leptons also some
kind of shell structure.