The costal margin, also known as the costal arch,[1] is the lower edge of the chest (thorax) formed by the bottom edge of the rib cage.

[2] The costal margins somewhat protect the higher abdominal organs, such as the liver.

[4][5] The costal margin may be used for tissue harvesting of cartilage for use elsewhere in the body, such as to treat microtia.

[4] Different abdominal organs may be palpated just below the costal margin, such as the liver on the right side of the body.

[5] Pain across the costal margin is most commonly caused by costochondritis.