HOK (formerly Hellmuth, Obata + Kassabaum) is a global architecture, interiors, engineering, planning and consulting firm. HOK is the largest U.S.-based architecture-engineering firm and the world's fourth-largest architectural firm. HOK is also the country's leading design firm in terms of non-U.S. fee growth and the second-largest interior design firm. As of 2009, the firm maintains more than 2,000 professional staff across a global network of 24 offices and is active in all major architectural specialties.