Actelion (SIX: ATLN) is a Swiss biotech firm. It has subsidiaries with marketing and sales in more than 30 countries, covering all key pharmaceutical markets worldwide. It is the largest biotechnology company in Europe.

It is a leader in the field of pulmonary arterial hypertension (PAH). Actelion's portfolio of PAH treatments covers the spectrum of disease, from WHO Functional Class (FC) II through to FC IV, with oral, inhaled and intravenous medications. Although not available in all countries, Actelion has treatments approved by health authorities for a number of specialist diseases including Type 1 Gaucher disease, Niemann-Pick type C disease, Digital Ulcers in patients suffering from systemic sclerosis, and mycosis fungoides in patients with cutaneous T-cell lymphoma.