Also known as bilva or wood apple (Aegle marmelos), the bel is a medium-sized deciduous tree. It has thorny branches and trifoliate leaves. Its fruit is large and round with a greenish-grey, woody shell. The bel has medicinal properties. Its leaves make poultice for the eyes and are good for diabetes and the roots help reduce fever. Its fruit is a remedy for dysentery. It is also believed to promote fertility.

Its leaves are an important offering to Shiva, for their trifoliate shape signifies Shiva's three eyes. Since they have a cooling effect, they are offered to the Shivalinga to soothe this hot-tempered deity. Even a fallen bel is never used as firewood, for fear of arousing Shiva's wrath. Its wood is used only in sacrificial fires.

According to the Agni Purana, on any auspicious day in Bhadra, Shiva should be worshipped with a daylong fast and the eating of bel leaves at night (see Vrata).

The Padma Purana and the Brahma Purana say that Shiva once hid in the bel to escape conquering demons (see Sacred Trees).

The Skanda Purana holds that the bel grew from Parvati's perspiration, which fell to the ground while she performed penance. It also says that the various incarnations of Parvati reside in each part of the tree. The Brihaddharma Purana relates how Lakshmi prayed to Shiva every day and offered him 10,000 lotus buds. One day she fell short by two buds. Remembering that Vishnu had compared her breasts to lotus buds, she decided to offer them instead. She cut one off and offered it humbly. Before she could cut the other, Shiva, pleased with her devotion, stopped her. Her cut breast became the fruit of the bel. The Bhavishya Purana says that after the samudra manthan, Lakshmi, who had just emerged from the ocean, rested in the bel. It was the ninth bright day of Bhadra. Therefore, the bel is worshipped every year on that day.