IUBS is established, following the recommendations of the "Conférences des Académies Scientifiques Interalliées", held in Brussels, Belgium.
Statutes and structure are formalised.
IUBS is formally admitted as a member of the International Research Council, which is now the International Council of Scientific Unions (ICSU).
The Union’s two major fields of activity are the promotion of scientific information and the environment. Its information project is later developed into "UNISIST", and its work on environmental issues contributes towards establishment of the World Conservation Union (IUCN). New ideas are pursued in the areas of evolution and genetics.
During World War II the Union is inactive.
With modern biological disciplines, such as evolutionary biology, genetics, cell biology ecology and developmental biology, coming to the fore, IUBS develops into an exemplary international forum for biology. The International Biological Programme IBP is initiated by IUBS, then taken over and coordinated by ICSU. This is the first serious effort to develop an international programme in the life sciences.
This period witnesses the creation of many IUBS scientific programmes of a multidisciplinary nature – Decade of the Tropics, Bioindicators, Biological Complexity, Biological Diversity. (cf. Accomplished Programmes)
The development of IUBS Scientific Programmes continues in the Nineties, with the birth of Diversitas, Biosystematics, Species 2000, Bionomenclature, Reproductive Biology and Aquaculture. The IUBS 26th General Assembly, held in 1997 in Taipei, adopts a new programme "Towards an Integrative Biology" TAIB. (cf. Current Programmes)