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A modular tensor category provides the appropriate data for the construction of a threedimensional topological ﬁeld theory. We describe the following analogue for two-dimensional conformal ﬁeld theories: a 2-category whose objects are symmetric special Frobenius algebras in a modular tensor category and whose morphisms are categories of bimodules. This 2-category provides sufﬁcient ingredients for constructing all correlation functions of a two-dimensional rational conformal ﬁeld theory. The bimodules have the physical interpretation of chiral data, boundary conditions, and topological defect lines of this theory.