An unloading system (130;430) for unloading bookbinding items into stacks each comprising one or more of the bookbinding items, wherein the unloading system (130;430) comprises: a sequence of a plurality of stackers (135a-135c;435a-435c) for stacking the bookbinding items provided by corresponding bookbinding machines (105a-105c;405a-405c) into corresponding stacks, each successive one of the stackers (135b-135c;435b-435c) different from a first one of the stackers (145a;435a) in the sequence comprising: a transit zone for a transit of corresponding stacks, a stacking zone of the corresponding bookbinding items in the corresponding stacks arranged above the transit zone in condition of use thereby not interfering with the transit of the stacks, and a support element openable to drop each of the corresponding stacks from the stacking zone into the transit zone, the unloading system being characterised in that each successive one of the stackers different from a first one of the stackers in the sequence further comprises a condition detector for detecting a condition of the stacking zone, and in that the unloading system (130;430) further comprises: corresponding one or more transit conveyors (145ab-145bc) for the successive stackers (135b-135c;435b-435c), each for conveying corresponding stacks from a previous one of the stackers (135a-135b;435a-435b) in the sequence to the transit zone of the corresponding successive stacker (135b-135c;435b-435c), corresponding one or more stop elements for the transit conveyors (145ab-145bc), each for stopping the corresponding stacks on the corresponding transit conveyor (145ab-145bc) upstream of the corresponding transit zone, corresponding one or more presence detectors for the stop elements, each for detecting a presence of the corresponding stacks being stopped by the corresponding stop element, an unloading conveyor for conveying the stacks from a last one of the stackers (135c;435c) in the sequence to an unloading zone of the stacks, and a control system (155b-155c;455b-455c), for each of the successive stackers (135b-135c;435b-435c) the control system (155b-155c;455b-455c) being configured to control the support element and the stop element according to the condition of the stacking zone, the presence of the corresponding stacks and a current operating speed of the corresponding bookbinding machine (105b-105c;405a-405c). a transit zone for a transit of corresponding stacks, a stacking zone of the corresponding bookbinding items in the corresponding stacks arranged above the transit zone in condition of use thereby not interfering with the transit of the stacks, and a support element openable to drop each of the corresponding stacks from the stacking zone into the transit zone, the unloading system being characterised in that each successive one of the stackers different from a first one of the stackers in the sequence further comprises a condition detector for detecting a condition of the stacking zone, and in that the unloading system (130;430) further comprises: corresponding one or more transit conveyors (145ab-145bc) for the successive stackers (135b-135c;435b-435c), each for conveying corresponding stacks from a previous one of the stackers (135a-135b;435a-435b) in the sequence to the transit zone of the corresponding successive stacker (135b-135c;435b-435c), corresponding one or more stop elements for the transit conveyors (145ab-145bc), each for stopping the corresponding stacks on the corresponding transit conveyor (145ab-145bc) upstream of the corresponding transit zone, corresponding one or more presence detectors for the stop elements, each for detecting a presence of the corresponding stacks being stopped by the corresponding stop element, an unloading conveyor for conveying the stacks from a last one of the stackers (135c;435c) in the sequence to an unloading zone of the stacks, and a control system (155b-155c;455b-455c), for each of the successive stackers (135b-135c;435b-435c) the control system (155b-155c;455b-455c) being configured to control the support element and the stop element according to the condition of the stacking zone, the presence of the corresponding stacks and a current operating speed of the corresponding bookbinding machine (105b-105c;405a-405c). corresponding one or more transit conveyors (145ab-145bc) for the successive stackers (135b-135c;435b-435c), each for conveying corresponding stacks from a previous one of the stackers (135a-135b;435a-435b) in the sequence to the transit zone of the corresponding successive stacker (135b-135c;435b-435c), corresponding one or more stop elements for the transit conveyors (145ab-145bc), each for stopping the corresponding stacks on the corresponding transit conveyor (145ab-145bc) upstream of the corresponding transit zone, corresponding one or more presence detectors for the stop elements, each for detecting a presence of the corresponding stacks being stopped by the corresponding stop element, an unloading conveyor for conveying the stacks from a last one of the stackers (135c;435c) in the sequence to an unloading zone of the stacks, and a control system (155b-155c;455b-455c), for each of the successive stackers (135b-135c;435b-435c) the control system (155b-155c;455b-455c) being configured to control the support element and the stop element according to the condition of the stacking zone, the presence of the corresponding stacks and a current operating speed of the corresponding bookbinding machine (105b-105c;405a-405c).