Gibberellins are a group of plant hormones, mainly found in the seeds, young leaves, and roots of green plants and certain fungi. They were originally isolated from a Japanese fungus (Gibberella fujikuroi) which lengthens the stems of rice plants. Gibberellins stimulate cell division, stem elongation, the breaking of dormancy (by triggering the production of enzymes essential for germination) and response to light and temperature. They interact with some auxins to promote cell enlargement and have been used to increase crop yields substantially.

Gibberellic acid, found in green plants, is involved in the "bolting" of plants like carrots.