Abstract: A hinge assembly for use on a spray boom attached to a sprayer apparatus. This hinge assembly allows the inner and outer boom members to pivot in both the horizontal and vertical planes. The hinge assembly has three primary components the first of which is the boom knuckling hinge. The boom knuckling hinge is the component which allows the outer boom assembly to pivot in the vertical plane. The second component of the hinge assembly is the breakaway portion. This component allows the outer boom to flex in the horizontal plane and in a rearward manner when an obstacle or the ground is inadvertently struck by the outer boom during normal operation. The third and last component of the hinge assembly is the boom folding apparatus. The folding apparatus is used to fold the outer boom against the inner boom for transport and storage purposes. This is accomplished by the use of two hydraulic cylinders, one on each the inner and outer booms, that are attached to the boom hinge.