[en] The scissors-like magnetic dipole excitations, know to be peculiar to deformed nuclei are first investigated. Its collective properties, like close correlation with the ground state quadrupole collectivity, are analysed in a unified context which encompasses semiclassical, algebraic and schematic models. Its single particle features, like the fragmentation of the M1 strength, are described in random-phase approximation and in the quasiparticle-phonon nuclear model. The properties of the spin excitations in deformed nuclei are also discussed. Finally, the effect of deformation on orbital and spin magnetic quadrupole transitions in heavy nuclei investigated. (author)