Narrow-leaved helleborine  – Cephalanthera longifolia,
is a herbaceous perennial plant with rhizomes of the family Orchidaceae. It is native to light woodland, widespread across Europe, Asia and North Africa from Ireland and Morocco to China. This includes Iran, Russia, Kazakhstan, Turkey, Algeria, India, Pakistan, Germany, Italy, France, Spain, Portugal and many other countries.

Narrow-leaved helleborine  reaches on average 20–60 centimetres (7.9–23.6 in) of height in typical conditions. This orchid has erect and glabrous multiple stems. The leaves are dark green, long and narrowly tapering (hence the common name of Sword-leaved Helleborine). The inflorescence is a lax, five to twenty-flowered spike with the bell-shaped flowers ascending in an oblique spiral. The flowers are white, about 1 cm (0.4 in) long, with a yellow-edged labellum and they usually open only during the warmest and brightest hours of the day. This plant can be found in bloom from April to June, depending on location and altitude. The fruit is a dry capsule and the dust-like seed is dispersed by the wind.

One unusual characteristic of this species is that some individuals are achlorophyllous (lacking green pigment) and take all their nutrition from mycorrhizal fungi.