A gearbox (1) for agricultural and industrial motor vehicles comprises an input shaft (2) and an output shaft (3), a first clutch (12) and a second clutch (13) arranged in a position between the first and second transmission shafts (16, 17), the first and second transmission shafts both being hollow. The gearbox further comprises a first intermediate shaft (20) and a second intermediate shaft (21), the first intermediate shaft extending coaxially inside the second intermediate shaft. A first engaging device (22) is capable of selectively connecting the first intermediate shaft to the output shaft, a second engaging device (23) is capable of selectively connecting the second intermediate shaft to the output shaft and a third engaging device (24) alternately connects the second intermediate shaft to the first intermediate shaft or to the output shaft. The first engaging device and second engaging device are coaxial with the output shaft. The third engaging device is coaxial with the first and second intermediat
