<p><i>Alnus glutinosa</i> (Betulaceae), commonly known as black alder, is a traditional medicinal tree with ecological, ethnobotanical, and pharmacological importance. This review presents the first comprehensive assessment of its medicinal potential, integrating botanical background, phytochemistry, and bioactivities. Scientific investigations have validated the traditional applications and revealed diverse pharmacological properties, including anticancer, antioxidant, antibacterial, antifungal, anti-inflammatory, hepatoprotective, and wound-healing effects. These effects can be attributed, in large part, to bioactive chemical compounds such as diarylheptanoids, flavonoids, phenolics, tannins, terpenoids, and steroids. These constituents modulate oxidative stress, inflammatory pathways, and other important cellular functions. This work highlights the therapeutic value of <i>A. glutinosa</i> and exposes crucial gaps in knowledge by combining chemical composition with pharmacological insights. Specifically, the work focuses on the relationship between the two. In particular, additional mechanistic investigations and clinical validation are required in order to advance its function in contemporary medical practice. Overall, the review provides a foundation for future studies on <i>A. glutinosa</i>, supporting its potential as a promising source of bioactive compounds for drug development.</p><p></p>