A green wall is a wall, either free-standing or part of a building, that is partially or completely covered with vegetation and, in some cases, soil or an inorganic growing medium. The concept of the green wall dates back to 600 BC with the Hanging Gardens of Babylon. The modern green wall with integrated hydroponics was invented by Stanley Hart White at the University of Illinois Urbana-Champaign in 1931-38. White holds the first known patent for a green wall, or vertical garden, conceptualizing this new garden type as a solution to the problem of modern garden design. More recently, the larger green walls concept has been utilized with innovative hydroponics technology. The vegetation for a green façade is always attached on outside walls; with living walls this is also usually the case, although some living walls can also be green walls for interior use. While Patrick Blanc is sometimes credited as having developed the concept in the late 1980s, the actual inventor is Stanley Hart White, a Professor of Landscape Architecture who patented a green wall system in 1938.
There are two main categories of green walls: green façades and living walls. Green façades are made up of climbing plants either growing directly on a wall or, more recently, specially designed supporting structures.