The batching problem is part of planning for order picking. Orders are received and subsequently released for fulfillment. Given a set of released orders, the problem is to partition the set into batches, where each batch will be picked and accumulated for packing and shipping during a specific time window, or ‘‘pick wave.’’ The time required to pick the items in any batch should not exceed the time window or pick wave duration. If zone picking is employed, the batch should balance pick effort across the zones to achieve high picker utilization, while minimizing pick time so that the number of pickers required is minimized.