Process for the preparation of (co) polymers of conjugated dienes which comprises polymerizing at least one conjugated diene in the presence of a catalytic system comprising at least one bis-imino-pyridine complex of cobalt having general formula (I) : wherein : R 2 and R 3 , equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C 1 -C 20 preferably C 1 -C 15 , alkyl groups, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; R 1 and R 4 , different from each other, represent a hydrogen atom; or they are selected from linear or branched C 1 -C 20 preferably C 1 -C 15 , alkyl groups, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; arylalkyl groups; or R 1 and R 2 can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C 1 -C 20 , preferably C 1 -C 15 , alkyl groups, said cycle optionally containing other heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; or R 3 and R 4 , can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C 1 -C 20 , preferably C 1 -C 15 , alkyl groups, said cycle optionally containing other heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; R 5 , R 6 and R 7 , equal to or different from each other, represent a hydrogen atom, or they are selected from linear or branched C 1 -C 20 , preferably C 1 -C 15 , alkyl groups, optionally halogenated, cycloalkyl groups optionally substituted; aryl groups optionally substituted; arylalkyl groups; or R 5 and R 6 , can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C 1 -C 20 , preferably C 1 -C 15 , alkyl groups, said cycle optionally containing other heteroatoms such as, for example, oxygen, -sulfur, nitrogen, silicon, phosphorous, selenium; or R 6 and R 7 , can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C 1 - C 20 , preferably C 1 -C 15 , alkyl groups, said cycle optionally containing other heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; X 1 and X 2 , equal to or different from each other, represent a halogen atom such as, for example, chlorine, bromine, iodine; or they are selected from linear or branched C 1 -C 20 , preferably C 1 -C 15 , alkyl groups, -OCOR 8 groups or -OR 8 groups wherein R 8 is selected from linear or branched C 1 -C 20 / preferably C 1 -C 15 , alkyl groups.