The pectoralis major (from Latin pectus 'breast') is a thick, fan-shaped or triangular convergent muscle of the human chest. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor muscle. The pectoralis major arises from parts of the clavicle and sternum, costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle; it inserts onto the lateral lip of the bicipital groove. It receives double motor innervation from the medial pectoral nerve and the lateral pectoral nerve. The pectoralis major's primary functions are flexion, adduction, and internal rotation of the humerus. The pectoral major may colloquially be referred to as "pecs", "pectoral muscle", or "chest muscle", because it is the largest and most superficial muscle in the chest area.

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