Formoterol (INN) or eformoterol (former BAN) is a long-acting β₂-agonist used in the management of asthma and/or chronic obstructive pulmonary disease (COPD). It is marketed in both dry-powder inhaler (DPI) and metered dose inhaler (MDI) preparations, under various trade names including Foradil/Foradile (Novartis) and Oxis (AstraZeneca).

Formoterol is a long-acting β₂ agonist (LABA), which has an extended duration of action (up to 12 hours) compared to short-acting β₂ agonists such as salbutamol, which have are effective for 4–6 hours. LABAs such as formoterol are used as "symptom controllers" to supplement "preventer" corticosteroid therapy (e.g. fluticasone). A "reliever" short-acting β₂ agonist (e.g. salbutamol) is still required, since LABAs are not recommended for the treatment of acute asthma.

Inhaled formoterol works like other β₂-agonists, causing bronchodilatation by relaxing the smooth muscle in the airway so as to treat the exacerbation of asthma. The long duration of formoterol action occurs because the formoterol molecules initially diffuse into the plasma membrane of the lung cells, and then are slowly released back outside, where they can come into contact with β₂ adrenergic receptors. Formoterol has been demonstrated to have a faster onset of action than salmeterol as a result of lower lipophilicity, and has also been demonstrated to be more potent - a 12 µg dose of formoterol has been demonstrated to be equivalent to a 50 µg dose of salmeterol.