Quantum-field theories as representations of a single ${}^{\ast }$-algebra

We show that many well-known quantum field theories emerge as representations of a single ${}^{\ast }$-algebra. These include free quantum field theories in flat and curved space-times, lattice quantum field theories, Wightman quantum field theories, and string theories. We prove that such theories can be approximated on lattices, and we give a rigorous definition of the continuum limit of lattice quantum field theories.