We provide a description of even-even N = Z nuclei in a formalism of quartets. Quartets are four-body correlated structures characterized by isospin T and angular momentum J. We show that the ground state correlations induced by a realistic shell model interaction can be well accounted for in terms of a restricted set of T = 0 low–J quartets, the J = 0 one playing by far a leading role among them. A conceptually similar description of odd-odd self-conjugate nuclei is given in terms of two

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... ct families of building blocks, one formed by the same T = 0 quartets employed for the even-even systems and the other by collective pairs with either T = 0 or T = 1. Some applications of this formalism are discussed for nuclei in the sd shell.