This article introduces topological operators and the higher-form symmetries they generate. In d-dimensional spacetime, a topological operator nominally localized on a submanifold with q dimensions defines a symmetry that can affect some operators that are nominally localized on submanifolds with p dimensions, provided p+q≥ d-1 so that the submanifolds can be linked with each other in the knot-theoretic sense. This is called a p-form symmetry. This article explains the relationship between how these symmetries are described in the canonical and path integral formulations. Examples with p=0 (zero-form symmetry) and with p=1 (one-form symmetry) are given, including a one-form symmetry called center symmetry.
