Little is known about how auditor industry specialization operates when mandatory audit firm rotation is in place. We interview Big 4 partners in Italy, where mandatory audit firm rotation is in place, in order to learn more about how industry specialization is acquired, how it compares to other European countries, and any trends over the past decade. We learn several key points. Industry specialization exists at the national level and the local area level in Italy. Partners seem to desire retaining industry knowledge at the national level. Industry specialization is acquired by formal and informal training from partners and managers, consulting by expert personnel to audit teams, expert quality control reviewers assigned to audit engagements, and industry documentation. The U.S. and the U.K. have more industry specialization than Italy, and it is organized within each country. Industry specialization has increased over the past decade in Italy.