In general, a Declaration of Conformity is a statement by a manufacturer that its product or service conforms to a specific standard.
In the European Union, the Declaration of Conformity is the EC declaration of conformity in which it is declared that the device or system complies with a certain standard of conformity. Declarations of Conformity are always product-, process- or service-related and only apply to the corresponding product and the assurance of certain values, such as electromagnetic compatibility (EMC).
In the USA, the Declaration of Conformity (DoC) is a certification standard adopted by the US Federal Communications Commission (FCC) and issued for individual PC components and assemblies, such as the motherboard. The DoC certification is more stringent than other FCC guidelines, as the values for electromagnetic interference (EMI) can only be achieved with higher circuitry effort without a housing.