Abstract: Various embodiments of a system and method for directing indicator-based sortation of shipments are described. In various embodiments, a control system may be configured to utilize indicators to direct the sortation of items in a materials handling facility, such as an order fulfillment center tasked with fulfilling customer orders for one or more items. For a given unsorted item, the control system may cause an indicator to indicate to which of multiple sorting slots the given item is to be placed, thereby sorting the item to its respective shipment assigned to the sorting slot. In various embodiments, the shipment sorting units may be serviced from a rebin side as well as a pack side. The control system may be configured to prioritize the processing of such shipments by utilizing indicators associated with respective shipment sorting slots on the pack side to indicate a priority for processing a given shipment.