The symbol of Expo '67, Buckminster Fuller's sphere is a landmark in the history of contemporary architecture and the most important building of its kind in the world. Its structure reproduces more than 97% of a sphere (62.8 metres in height and 76.2 metres in diameter).

The original structure was covered with 1,900 transparent acrylic panels.

The building's complete transparency created an almost invisible barrier between the inside and the outside. In 1976, while the structure was being repaired, a fire broke out and completely destroyed the acrylic skin. Only the tubular frame remained intact.

The outer shell of the Biosphère was awarded to Buckminster Fuller (1895-1983), who called himself a "comprehensive anticipatory design scientist", but the design of the US pavilion's inner structure was given to Cambridge Seven Associates Inc., a group of Harvard University architecture and design professors.

The original inner structure consisted of four large platforms divided into seven levels and connected by escalators, bridges and elevators. During Expo '67, the gigantic structure included a 37.5-metre (123-foot) escalator. The longest escalator ever built, it was the equivalent of eight floors.

In 1990, Environment Canada signed an agreement with the City of Montreal to convert the structure into a site devoted to eco-action. Montreal architect Éric Gauthier won an architectural competition and was commissioned to convert the interior structure in keeping with the original design, in line with Fuller's avant-garde philosophy: seeking maximum efficiency for minimum effort.

Since its opening in 1995, Environment Canada's Biosphère has been a showcase for environmental education. As an Environment Museum, the Biosphère raises the awareness of young people and their families, and the general public about major environmental issues, including those related to water and climate change, and the sustainable development, through exhibitions, interactive activities and multimedia presentations.