A drive system for an aircraft landing gear is described. The drive system includes a drive pinion, a drive shaft arranged to rotate the drive pinion about a drive axis, and a casing which rotatably supports the drive shaft. The drive pinion is rotatably supported on the casing by a self-aligning bearing. The drive pinion is coupled to the drive shaft by a flexible coupling adapted to transfer torque between the drive pinion and the drive shaft and to permit tilting of the drive pinion relative to the drive axis.