Interdisciplinarity is when two or more subjects (academic disciplines) join up. This happens when a problem overlaps traditional academic boundaries. Other terms which mean almost the same thing are multidisciplinarity and crossdisciplinarity.

An examples makes clear what is meant:

• In order to investigate living cells, these subjects joined together: genetics, physics, chemistry, cytology.

When they joined up, the field they formed was called cell biology at the level of cells, or molecular biology at the level of macromolecules.

Other examples include artificial intelligence, cultural studies, cybernetics, computational linguistics, biomedical engineering, and so on. Physical chemistry, biochemistry and astrophysics must have been some of the first.