This paper introduces Symmetry Theory (SymTh), a framework for studying non-finite symmetries in quantum field theories (QFTs). Unlike SymTFTs, which are topological, SymTh is not topological and is inspired by holographic or geometric constructions in string theory. It involves a bulk theory with a coupling constant and is subject to renormalization. The framework focuses on topological operators and boundary conditions, allowing for the study of non-flat configurations of continuous symmetries, which are not automatically described by SymTFTs. The paper proposes a procedure analogous to the sandwich construction of SymTFTs to obtain the physical QFT. It applies this approach to various examples, including abelian p-form symmetries, 2-groups, and Q/Z non-invertible symmetries. The paper also discusses the derivation of SymTh for Q/Z non-invertible symmetries from the dimensional reduction of IIB supergravity on the conifold and provides an ultraviolet interpretation of quantum Hall states in terms of branes in the IIB supergravity background. The paper concludes with a discussion of the implications of these results for the study of symmetries in QFTs.This paper introduces Symmetry Theory (SymTh), a framework for studying non-finite symmetries in quantum field theories (QFTs). Unlike SymTFTs, which are topological, SymTh is not topological and is inspired by holographic or geometric constructions in string theory. It involves a bulk theory with a coupling constant and is subject to renormalization. The framework focuses on topological operators and boundary conditions, allowing for the study of non-flat configurations of continuous symmetries, which are not automatically described by SymTFTs. The paper proposes a procedure analogous to the sandwich construction of SymTFTs to obtain the physical QFT. It applies this approach to various examples, including abelian p-form symmetries, 2-groups, and Q/Z non-invertible symmetries. The paper also discusses the derivation of SymTh for Q/Z non-invertible symmetries from the dimensional reduction of IIB supergravity on the conifold and provides an ultraviolet interpretation of quantum Hall states in terms of branes in the IIB supergravity background. The paper concludes with a discussion of the implications of these results for the study of symmetries in QFTs.