The respiratory system supplies animals with oxygen and releases the carbon dioxide from metabolism.

The respiratory system of chickens consists of:
- nasal cavities
- larynx
- trachea (windpipe)
- syrinx (voice box)
- bronchi
- lungs
- air sacs (9 in total, two pairs thoracic and two pairs abdominal, one interclavicular)
- air-containing bones

Chickens have rather small lungs, which expand or contract only slightly, without a true diaphragm. Due to the skeletal construction of the breast, expansion is limited. The lungs are supported by the air sacs and a group of hollow, air-containing bones.

While the air freely moves in and out of the air sacs, only the lungs exchange oxygen and carbon dioxide. Both the lungs and the air sacs function as cooling mechanisms as moisture evaporates from their surfaces and is exhaled as water vapor.

The respiratory rate is governed by the carbon dioxide content of the blood. Increased levels increase the rate. In resting birds, respiratory rate levels range between 15 and 25 cycles/min.