An articulated harvester includes a powered harvester having a pair of forward wheels or tracks, having a pair of rotatable rearward caster wheels, and carrying an on-board harvester grain bin for housing harvested grain. The harvester tows a grain cart, which carries a grain cart bin for housing harvested grain. A joint assembly interconnects the harvester and the grain cart. The joint assembly includes a grain cart tongue that mates with the harvester. An articulation cylinder assembly connects the harvester and the grain cart tongue in the region of the joint assembly. Bi-directional, biased guide rods connect between the grain cart tongue and the caster wheels. The grain car may be steerable and/or powered. The harvester may be steerable by its pair of forward wheels or tracks. A conventional harvester and grain cart assembly can be converted into the novel articulated harvester.