This review covers the physiology and molecular biology of the plant beta-glucanases possessing either endo-1,3-beta-D-giucanase (EC 3.2.1.39) or endo-1,3;1,4-beta-D-glucanase (EC 3.2.1.73) activity. These beta-glucanases are structurally related enzymes that are believed to be involved in many important aspects of plant physiology and development, such as germination, growth, defense against pathogens, flowering, cellular and tissue development and differentiation, and probably other roles. They also are regulated by numerous plant hormones, biotic and abiotic elicitors and stresses, and they exhibit complex tissue- and developmental-specific gene expression.