A gearbox for agricultural and industrial motor vehicles comprising: - an input shaft and an output shaft; - a first clutch and a second clutch, of which the respective pulling portions (12A, 13A) are connected with torsional coupling to the input shaft and the respective pulled portions are connected to a respective first and second transmission shaft (16, 17), the first and second clutches (12, 13) being arranged in a position between the first and second transmission shafts (16, 17), the first and second transmission shafts (16, 17) both being hollow with the input shaft coaxial and internal with respect to the first transmission shaft; - a first intermediate shaft which can be connected to the first transmission shaft and to the output shaft by means of a first plurality of pairs of toothed wheels (4a, 4b, 8a, 8b, 9a, 9b, 10a, 10b) in mutual engagement and a second intermediate shaft which can be connected to the second transmission shaft and to the output shaft by means of a second plurality of pairs of toothed wheels (5a, 5b, 6a, 6b, 7a, 7b) in mutual engagement, the first intermediate shaft extending coaxially inside the second intermediate shaft, which is constructed in the form of a hollow shaft; - a first engaging device which is capable of selectively connecting the first intermediate shaft to the output shaft by means of a specific pair of toothed wheels (8a, 8b, 9a, 9b) of the first plurality; - a second engaging device which is capable of selectively connecting the second intermediate shaft to the output shaft by means of a specific pair of toothed wheels (6a, 6b) of the second plurality; wherein the first engaging device is coaxial with the output shaft and a toothed wheel of the second plurality of pairs of toothed wheels (5a, 5b, 6a, 6b, 7a, 7b) is rotationally integral with respect to the second transmission shaft, the second engaging device also being coaxial with the output shaft, characterized by - a third engaging device which is capable of selectively connecting the second intermediate shaft to the first intermediate shaft and to the output shaft, the third engaging device being coaxial with the first and second intermediate shafts (20, 21) and being interposed in an axial position between the first and second engaging devices (22, 23). - an input shaft and an output shaft; - a first clutch and a second clutch, of which the respective pulling portions (12A, 13A) are connected with torsional coupling to the input shaft and the respective pulled portions are connected to a respective first and second transmission shaft (16, 17), the first and second clutches (12, 13) being arranged in a position between the first and second transmission shafts (16, 17), the first and second transmission shafts (16, 17) both being hollow with the input shaft coaxial and internal with respect to the first transmission shaft; - a first intermediate shaft which can be connected to the first transmission shaft and to the output shaft by means of a first plurality of pairs of toothed wheels (4a, 4b, 8a, 8b, 9a, 9b, 10a, 10b) in mutual engagement and a second intermediate shaft which can be connected to the second transmission shaft and to the output shaft by means of a second plurality of pairs of toothed wheels (5a, 5b, 6a, 6b, 7a, 7b) in mutual engagement, the first intermediate shaft extending coaxially inside the second intermediate shaft, which is constructed in the form of a hollow shaft; - a first engaging device which is capable of selectively connecting the first intermediate shaft to the output shaft by means of a specific pair of toothed wheels (8a, 8b, 9a, 9b) of the first plurality; - a second engaging device which is capable of selectively connecting the second intermediate shaft to the output shaft by means of a specific pair of toothed wheels (6a, 6b) of the second plurality; - a third engaging device which is capable of selectively connecting the second intermediate shaft to the first intermediate shaft and to the output shaft, the third engaging device being coaxial with the first and second intermediate shafts (20, 21) and being interposed in an axial position between the first and second engaging devices (22, 23).