IAA (Indole-3-Acetic Acid) is the abundant and well known plant hormone of the auxin class. IAA is predominantly produced in the apical bud of and young leaves of plants and is known to be an inducer of cell division and elongation. IAA, as well as most other auxins, are also known to act in concert with, or in opposition to, other plant hormones. For example, the ratio of auxin to cytokinin in certain plant tissues determines initiation of root versus shoot buds.

IBA (Indole-3-butyric acid) is a plant hormone belonging to the auxin family and assists in initiating root formation; the in vitro process is called micropropagation. Aside from accelerating root formation, it is used on various crops to stimulate flower development and the growth of fruits. This ultimately increases crop yields.

Historically, products that contained IBA were used to protect plants during transplantation by stimulating root growth and decreasing shock.