Forsythia are deciduous shrubs typically growing to a height of 1–3 m (3 ft 3 in – 9 ft 10 in) and, rarely, up to 6 m (20 ft) with rough grey-brown bark. The leaves are borne oppositely and are usually simple, though sometimes trifoliate with a basal pair of small leaflets; they range between 2 and 10 cm (0.79 and 3.94 in) in length and, rarely, up to 15 cm (5.9 in), with a margin that is serrated or entire (smooth). Twigs may be hollow or chambered, depending on the species.

The flowers are produced in the early spring before the leaves, bright yellow with a deeply four-lobed flower, the petals joined only at the base. These become pendent in rainy weather thus shielding the reproductive parts. The fruit is a dry capsule, containing several winged seeds.