Methods and apparatus for stacking receptacles in materials handling facilities. An automated receptacle stacker may be integrated into a materials handling system to receive empty receptacles from upstream stations via an input conveyance mechanism, add the receptacles to a stack in a stack hopper, detect when the stack is complete, and output the stack onto an output conveyance mechanism. The output conveyance mechanism may convey the stack to a palletization station, and the stacker may begin another stack. This process may continue to build and output stacks of empty receptacles. In some implementations the receptacles may be stackable only when oriented correctly; in these implementations, orientation of the receptacles may be detected prior to stacking and incorrectly oriented receptacles may be either rotated to the correct orientation or diverted to a second receptacle stacker.