Acute or chronic instability and osteoarthritis of the acromioclavicular (ac) joint may cause significant impairment of the shoulder. In this continuing education report, the pathomorphology of acute ac dislocations is described based on the Rockwood classification. Decision making on conservative or surgical treatment is discussed. Surgical techniques are presented as acromioclavicular or coracoclavicular procedures. Persistent complaints may warrant additional surgical therapy after conservative treatment as well as after primary surgical treatment. In these cases, residual instability must be addressed. A modified Weaver-Dunn procedure is presented in detail. In any patient with shoulder pain, osteoarthritis of the ac joint has to be taken into consideration. Resection of the lateral clavicle has proved to be effective in these patients.