The interacting boson model introduced in Section 33 has been described from the point of view of the collective model of the nucleus. The 5 components of a d -boson have been related to the 5 degrees of freedom of a shape, with constant volume, which may have quadrupole deformations. The s -boson has been added to simplify the construction of eigenstates which belong to irreducible representations of the U (6) group, the fully symmetric ones being characterized by an integer N . We saw how simple Hamiltonians including single boson energies and boson boson interactions give very good description of various kinds of collective motion.