Reaction of CsF with ClF3 leads to Cs[Cl3F10]. It contains a molecular, propeller-shaped [Cl3F10]− anion with a central μ3-F atom and three T-shaped ClF3 molecules coordinated to it. This anion represents the first example of a heteropolyhalide anion of higher ClF3 content than [ClF4]− and is the first Cl-containing interhalogen species with a μ-bridging F atom. The chemical bonds to the central μ3-F atom are highly ionic and quite weak as the bond lengths within the coordinating XF3 units (X = Cl, and also calculated for Br, I) are almost unchanged in comparison to free XF3 molecules. Cs[Cl3F10] crystallizes in a very rarely observed AB structure type, where cations and anions are each pseudohexagonally close packed, and reside, each with coordination number five, in the trigonal bipyramidal voids of the other.