Package grouping unit for a packaging line operable to produce multipacks; the grouping unit (1) comprises a linear conveyor (9) operable to feed a succession of packages (2) at a first speed (V1); and at least one grouping assembly (6) formed by two sub-assemblies (12a, 12b); wherein each sub-assembly comprises a pair of endless conveyors (13a, 14a; 13b, 14b) and define, with the endless conveyors (13a, 14a; 13b, 14b) of the other sub-assembly (12b, 12a), a package grouping channel (22) having a package inlet (7) and a group outlet (8); each endless conveyor is provided with a number of package retaining elements (26); the endless conveyors are operable independently from each other to move a first retaining element (26) through the package inlet (7) at a second speed (V3) lower than the first speed (V1) so as to intercept and slow down a first package (2) in the succession and cause the packages (2) to group; and to move a second retaining element (26), carried by a different endless conveyor (13a; 14a; 13b; 14b), through the package inlet (7) so as to intercept the last package (2) in the succession and define, with the first retaining element (26), a seat that is so sized as to accommodate a package group (3) and is movable, with the package group (3), along the grouping channel (22).