A C*-algebra is a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = b* a* and the C*-identity ‖a* a‖ = ‖a‖². Related tags: [banach-algebras], [von-neumann-algebras], [operator-algebras], [spectral-theory].

A C*-algebra is a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = *b** *a** and the C*-identity ‖ *a** a ‖ = ‖ a ‖2.

For bounded operators on a given Hilbert space, C*-algebras characterize topologically closed subalgebras of ${\mathcal B}({\mathcal H})$ (in operator norm), also closed under taking the adjoint operator. C*-algebras are at the heart of and are extensively used in .

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