The Willis Building (originally the Willis Faber & Dumas regional headquarters) in Ipswich, Suffolk, England, is one of the earliest buildings designed by Norman Foster and Wendy Cheesman after establishing Foster Associates. Constructed between 1970 and 1975 for the insurance firm now known as Willis Towers Watson, it is widely considered a landmark in the development of the 'high tech' architectural style. The building houses some 1,300 office staff in open-plan offices spread over three floors.

The bulbous floor plan of the office block reflects the layout of the available site in the centre of Ipswich, which is sandwiched between several road junctions and the Grade I listed Unitarian Meeting House, one of Ipswich's oldest surviving buildings. Thus two of the town's Grade I listed buildings stand side by side.

The centre of the building is constructed from a grid of concrete pillars, 14 m (46 ft) apart, supporting cantilevered concrete slab floors. The curtain wall exterior is clad in panels of dark smoked glass. The use of dark glass, a curtain wall and lack of right angle corners mirrors the art deco Express Building in Manchester, cited by Norman Foster as one of his favourite buildings and a design influence. The central escalator well leads up to a rooftop staff restaurant surrounded by a rooftop garden (360 panorama).

Originally, there was also a swimming pool for employees to enjoy during their lunch break. This has now been covered up (and preserved, rather than filled in, due to it being a listed building) and the space is used for more offices. The swimming pool can be seen underneath the false floor.

The Willis Building was commissioned by John Roscoe, chairman of Willis, Faber & Dumas, in the early 1970s. The architectural firm of Norman Foster was selected after a shortlist was provided by the Royal Institute of British Architects. Foster's design, inspired by a glass-clad office building he had recently completed, featured innovative energy-conscious elements and open-plan floor spaces. The building was officially opened on June 2, 1975, by former Prime Minister Harold Macmillan.

In 1991 the Willis building became the newest building to be given Grade I listed building status in Britain. At the time it was one of only two listed buildings under 30 years of age.

• List of tallest buildings and structures in Ipswich

• ConcreteCentre.com

• BBC Four episode of series Building Sights on the Willis Building, presented by Zaha Hadid
• Project description from Foster + Partner
• Map sources for Willis Building, Ipswich
• Historic England. "Details from listed building database (1237417)". National Heritage List for England.

52°03′20″N 1°09′03″E / 52.0556°N 1.1507°E / 52.0556; 1.1507