Patrick MacLeamy (chairman/CEO)William Hellmuth (president)
As of 2013, HOK is the largest U.S.-based architecture-engineering firm and the third-largest interior design firm. The firm maintains more than 1,600 professional staff across a global network of 24 offices and is active in all major architectural specialties. Its senior leaders are located in several different locations across the world.
HOK was established St. Louis, Missouri, in 1955. The firm's name is derived from the surnames of its three founding partners: George Hellmuth, Gyo Obata and George Kassabaum, all graduates of the School of Architecture at Washington University in St. Louis. The design firm started with 26 employees and its three founders.
The practice's first building designs were schools in St. Louis suburbs, and St. Thomas Aquinas High School in Florissant was the first private/parochial school designed by the firm. Another prominent school they designed was the Saint Louis Priory School. By the mid-1960s, the firm was winning commissions across the United States and began to open additional offices, starting with San Francisco in 1966 for the design of a library at Stanford University and Dallas in 1968 for the master planning and design of Dallas-Fort Worth International Airport. Also in 1968, HOK launched its interior design practice. HOK also expanded into Washington, DC, after winning the commission to design the Smithsonian National Air and Space Museum. In 1973, HOK established a presence in New York by acquiring Kahn & Jacobs, designers of many New York City skyscrapers. By the 1970s, the firm was operating internationally and in 1975 the firm was named as architect of the $3.5 billion King Saud University in Riyadh, at the time the single largest building project in the world. In 1979, George Kassabaum was elected into the National Academy of Design as an Associate Academician.
In 1983, HOK formed HOK Sport Venue Event, which became a leader in designing sport stadiums, arenas and convention centers. In January 2009, the Board of HOK Group, Inc. and managers of HOK Sports Facilities, LLC transferred ownership of HOK Sport to leaders of that practice. The company became an independent firm, and rebranded itself as Populous.
HOK's first office outside the United States opened in Hong Kong in 1984. In 1987, the firm opened a London office and then, in 1995, expanded this London practice by merging with renowned UK architectural practice Cecil Denny Highton. In November 1994, HOK acquired CRSS Architects, Inc. based in Houston, Texas, adding offices in Houston and Atlanta. HOK established its first offices in Canada (Toronto and Ottawa) in 1997 with the acquisition of Urbana Architects.
By 2007, international work represented more than 40% of HOK's annual revenue.
In 2012, HOK Chairman Bill Valentine retired after 50 years with the firm. HOK Chief Executive Officer Patrick MacLeamy, FAIA, assumed the role of chairman.
In 2012, HOK's London office faced a pre-tax loss of £935,500. The number of people employed in HOK's London office dropped from 172 to 157 during that period. In a statement, finance director Andrew Childs said, "This reduction reflected the parlous state of the construction industry in the UK." 
In 2013, HOK acquired the New York and Shanghai offices of hospitality design firm BBG-BBGM, creating one of the largest interior design firms. BBG-BBGM's office in Washington, D.C. continues to operate as BBGM.
In 2014, HOK announced plans to acquire 360 Architects and establish a new sports and entertainment practice. 360 Architects has 180 employees and offices in Kansas City, San Francisco and Columbus, Ohio. The merger is expected to close by the end of October 2014. 
Innovation and sustainable design
In 1983 HOK introduced HOK Draw, computer-aided drafting software products that specialized in conceptual architectural design. More recently,[when?] HOK uses Building Information Modeling (BIM) to streamline the design and construction process. In 2012, Building Design + Construction ranked HOK the No. 1 BIM Architecture Firm. In 2013, DesignIntelligence magazine, based in part on the firm's leadership in buildngSMART and BIM, ranked HOK the No. 1 Design Firm for Technology Expertise.
HOK is a leader in sustainable design. Professionals in the firm authored one of the industry's most respected resources on the topic, "The HOK Guidebook to Sustainable Design," originally published in 2000 by John Wiley & Sons. A second edition of the book was published in 2005. In September 2008, to better integrate nature's innovations into the design of buildings, communities and cities worldwide, HOK announced an alliance with the Biomimicry Group, co-founded by Janine Benyus. In 2010, HOK and energy and daylighting consultant The Weidt Group completed design of Net Zero Court, a 170,735-square-foot, market-rate, zero-emissions class A commercial office building in St. Louis.
In 2013, for the fourth consecutive year, the DesignIntelligence journal ranked HOK as a leader in sustainable and high-performance design". HOK currently has more than 900 LEED (Leadership in Energy and Environmental Design) credentialed professionals and 169 LEED, BREEAM, Green Mark and Green Globe certified projects.
In 2013, HOK and Biomimicry 3.8 released the Genius of Biome report, a textbook for how to apply biomimicry design principles.
United States: Atlanta, Chicago, Dallas, Denver, Houston, Los Angeles, Miami, New York, St. Louis, San Francisco, Seattle, Tampa, Washington, DC
Canada: Calgary, Ottawa, Toronto, Vancouver
Asia Pacific: Beijing, Hong Kong, Shanghai, Singapore
Europe: London, HOK Euronet - affiliated firms in Amsterdam, Brussels, Madrid, Milan, Paris and Rome
Middle East: Dubai
Dispute over proposed LG corporate headquarters
Beginning in January 2013, HOK’s design for the planned North American corporate headquarters of LG Electronics became the subject of legal and political controversy. The proposed 143-ft tower, to be constructed in Englewood, NJ, would rise several stories above the treeline of the Palisades, a National Natural Landmark. The tower project requires a variance and changes to local zoning laws, which historically have prohibited buildings above 35 feet to protect the view.
Advocacy groups and government officials from New York and New Jersey have heavily protested the proposed tower and filed lawsuits in NJ Superior Court, fighting changes made to zoning laws to permit the tower’s construction. Critics have suggested that a lower building could be redesigned on the 27-acre site. LG responded by stating that a redesign would “severely delay the economic and community benefits the new building will bring to the region.”
- 1962: The Priory Chapel, St. Louis, Missouri, United States
- 1970: Houston Galleria, Houston, Texas, United States
- 1970: Xerox PARC, Palo Alto, California, United States
- 1975: King Saud University, Riyadh, Saudi Arabia
- 1976: National Air and Space Museum, Washington, D.C., United States
- 1979: Cecil H. Green Library, Stanford University, Palo Alto, California, United States
- 1981: Moscone Center, San Francisco, California, United States
- 1981: Metropolitan Square, St. Louis, Missouri, United States – Current location of HOK St. Louis office
- 1982: Levi's Plaza, San Francisco, California, United States
- 1983: King Khaled International Airport, Riyadh, Saudi Arabia
- 1985: St. Louis Union Station Renovation and Redevelopment, St. Louis, Missouri, United States
- 1986: BP Building Cleveland, Ohio, United States
- 1986: Kellogg Company Headquarters Battle Creek, Michigan, United States
- 1986: Riverchase Galleria Birmingham, Alabama, United States
- 1991: 801 Grand, Des Moines, Iowa, United States (tallest building in Iowa)
- 1992: Schapiro Center for Engineering and Physical Science Research (CEPSR), Columbia University, New York City, United States
- 1993: Apple Inc. R&D Campus, Cupertino, California, United States
- 1994: Independence Temple, Independence, Missouri, United States
- 1995: Tokyo Telecom Center, Tokyo, Japan (co-designers)
- 1996: Tuntex Sky Tower, Kaohsiung, Taiwan
- 1996-1997: Nortel Brampton Centre HQ, Brampton, Ontario, Canada
- 1997: Foreign and Commonwealth Office Restoration, London, England
- 1997: George Bush Presidential Library, College Station, Texas, United States (on the campus of Texas A&M University)
- 1999: Northwestern Memorial Hospital Facility Replacement and Redevelopment, Chicago, Illinois, United States (co-designers)
- 1999: Edificio Malecon Office Tower, Buenos Aires, Argentina
- 1999: Boeing Leadership Center, St. Louis, Missouri
- 2000: Passenger Terminal Amsterdam, Amsterdam, The Netherlands
- 2001: United States Environmental Protection Agency Research Center, Research Triangle Park, North Carolina, United States (1.2 million-sq.-ft. campus)
- 2002: Darwin Centre at the Natural History Museum, Passenger Terminal Cork, Cork Airport, Ireland
- 2002: Alfred A. Arraj U.S. Courthouse, Denver, Colorado, United States
- 2003: Steven F. Udvar-Hazy Center of the National Air and Space Museum, Chantilly, Virginia, United States
- 2004: Harlem Hospital Center Master Plan and Patient Pavilion, New York City, United States
- 2005: Cisco Systems Executive Briefing Center Interior Design, San Jose, California, United States
- 2005: Terminal A at Logan International Airport, Boston, Massachusetts, United States (world's first LEED certified air terminal building)
- 2006: Lavasa Hill Station Master Plan and Design Guidelines, Moss Valley, Pune, India
- 2006: Natural History Museum of the Adirondacks (The Wild Center), Tupper Lake, New York, United States
- 2006: SJ Berwin European Headquarters Interior Design, London, England, (Business Week/Architectural Record Award winner)
- 2007: Dubai Marina, Dubai, United Arab Emirates
- 2007: Hyatt on the Bund, Shanghai, China
- 2008: Frost Art Museum, Florida International University, Miami, Florida, United States
- 2008: Midfield Terminal at the Indianapolis International Airport, Indianapolis, Indiana, United States (master designer)
- 2009: Doha City Centre, Doha, Qatar, (design of five hotel towers for largest retail development in the Middle East)
- 2009: King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia (Saudi Arabia's first LEED certified project and the world's largest LEED Platinum project)
- 2009: Carnival House, head office of Carnival UK, Southampton, England
- 2009: Bakrie Tower, Jakarta, Indonesia
- 2010: Indira Gandhi International Airport – Terminal 3, Delhi, India (LEED Gold certification)
- 2010: New Building 20 at NASA's Lyndon B. Johnson Space Center, Houston, Texas, (LEED Platinum certification)
- 2011: Salvador Dalí Museum, St. Petersburg, Florida
- 2011: Brigade Gateway Enclave, Bengaluru, India
- 2011: Keangnam Hanoi Landmark Tower, Hanoi, Vietnam (tallest building in Vietnam)
- 2012: Canon USA Headquarters, Melville, New York
- 2012: Baku Flame Towers, Baku, Azerbaijan
- 2012: Harlem Hospital Center Mural Pavilion, New York City
- 2013: Hamad International Airport Passenger Terminal Complex, Doha, Qatar
- 2013: Porsche U.S. Headquarters and Customer Experience Center, Atlanta, Georgia
- 2013: San Francisco Mint Adaptive Reuse, San Francisco, California
- 2013: Abu Dhabi National Oil Company Headquarters, Abu Dhabi, United Arab Emirates
- 2013: BBC Broadcasting House Headquarters Workplace Strategy and Interior Design, London, England
- 2014: Capital Market Authority Tower, Riyadh, Saudi Arabia
- 2014: 535 Mission Street, San Francisco, California, United States
- 2016: University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, New York
- 2016: Ri.MED Biomedical Research and Biotechnology Center, Palermo, Italy
- 2016: Perot Tower, Mixed Used, Dallas, Texas 
- "Top 300 Architecture Firms 2013', "Architectural Record", July 2013
- "2013 Top 100 Giants', "Interior Design", January 8, 2013.
- Dietsch, Deborah K. (November 17, 2008). "HOK's Bill Hellmuth: On top of the world".
- "Uncertain Economy Pushes Design Firms To Diversify Their Portfolios," Engineering News-Record", June 23, 2008.
- Rogers, David (8 October 2013). "HOK blames profits woe on UK business". bdonline. Retrieved 10 October 2013.
- Nalewicki, Jennifer (20 January 2014). "BBG-BBGM Joins HOK to Form Global Hospitality Leader". Interior Design magazine.
- "BBGM website".
- "HOK will acquire 360, restart sports architecture practice". Kansas City Business Journal. August 19, 2014.
- "BIM at HOK', "AEC Magazine", January 30, 2007.
- "BIM Finally Starting to Pay Off for AEC Firms', "Building Design + Construction", July 19, 2012.
- "2013 Technology Trends & Innovation Survey', "DesignIntelligence", May/June 2013.
- "HOK Earns Sustainable Leadership Award', "Interior Design", May 9, 2006.
- "HOK and Biomimicry Guild Forge Alliance for Bio-Inspired Design Excellence', "Treehugger.com", September 22, 2008.
- " New Zero: Two global design firms issue a call to action and lead by example, "Contract", October 2010.
- ["2013 Sustainable Design & Leadership Surveys], "DesignIntelligence", July/August 2013.
- " Genius of Biome Report: A Biomimicry Primer, "Treehugger", June 20, 2013.
- " The Cloister’s View Is Threatened By LG Electronics Offices, The New York Times, January 21, 2013.
- http://www.nydailynews.com/new-york/bronx/views-palisades-ruined-article-1.1427943" Decision by New Jersey judge will mar Bronx views of Palisades forever], The New York Daily News, August 15, 2013.