Besides iodine, few of the polyhalogen anions have been structurally characterized. Remarkably, the highest known ratio of elements‐to‐charge has now been found in the undecabromide [Br₁₁]⁻. This new polybromide monoanion has been prepared in pure halogen and was structurally characterized by single‐crystal X‐ray diffraction, Raman spectroscopy, and quantum‐chemical methods.