The mechanisms by which the transition to flowering is regulated in plants have been the subject of intense physiological study for many years. Recent studies, particularly in Arabidopsis thaliana, have revealed the genetic complexity of flowering. Flowering appears to be controlled by multiple pathways that are influenced by the environment in which the plant is grown as well as the developmental state of the plant. Several genes that regulate flowering time have been molecularly identified and the effects of altered expression of these genes have contributed greatly to understanding their role in flowering.