Most skin cancers can be managed effectively using standard therapeutic methods. However, specific subsets of skin cancers--including tumors that are recurrent, large, or aggressive, along with tumors located at sites of functional and cosmetic concern--provide a significant therapeutic challenge. Mohs micrographic surgery offers the greatest potential cor cure of difficult tumors, while providing for maximal preservation of healthy tissue. This paper describes the history of Mohs surgery, the technique, and the indications for its use.