A ventilated cage and rack system. An embodiment of the invention may comprise a ventilated rack, the rack including at least one air exhaust plenum and at least one canopy disposed within the rack, the canopy being adapted to position a cage assembly below the canopy while maintaining a gap between the top of the cage assembly so as to permit air to be drawn into the air exhaust plenum from the interior of the cage assembly through the top of the cage assembly and to also permit ambient air to be drawn across the top of the cage assembly into the air exhaust plenum. The cage assembly comprises one of a first cage having a first width and a plurality of second cages having a second width, the second width being less than the first width.