Normal scapular motion is closely integrated with arm motion to provide efficient scapulohumeral rhythm in shoulder function. This rhythm is often disrupted in patients with symptoms and signs of shoulder impingement. A large percentage of patients with shoulder impingement have scapular dyskinesis and alterations in the normal resting position of the scapula or in dynamic scapular motion. Scapular dyskinesis usually manifests as a loss of control in the motions of scapular external rotation and the translation of scapular retraction. This loss of control results in alteration in timing and magnitude of acromial upward rotation, excessive antetilting of the glenoid, and loss of maximal rotator cuff muscle activation capability. These pathophysiologic and pathomechanical alterations cause or increase the dysfunction associated with impingement. Scapular dyskinesis may have proximal or distal causative factors. Proximal factors are mainly associated with muscle factors, and can usually be treated with rehabilitation. Distal factors are mainly caused by internal derangements of joints and frequently require surgical treatment followed by appropriate rehabilitation. Physical examination techniques that specifically evaluate scapular dyskinesis can identify the causative factors and guide treatment and rehabilitation strategies.