Salix pentandra (bay willow) is a species of willow native to northern Europe and northern Asia.

It is a large shrub or small tree growing to 14 m (46 ft) tall (rarely to 17 m), usually growing in wet, boggy ground. The leaves are glossy dark green, 5-12 cm long and 2-5 cm broad, with finely serrated margins. The dioecious flowers are catkins, produced in late spring after the leaves; the male catkins are yellow, 2-5 cm long, the female catkins greenish, 1.5-3 cm long; they are pollinated by bees. The fruit is a small capsule containing numerous minute seeds embedded in white down which aids wind dispersal.