Definition
A Declaration of Conformity is a formal statement, signed by the manufacturer, that a product meets the requirements of the regulations that apply to it, and it is the manufacturer rather than a laboratory that carries the legal responsibility for it.
Explained in full

This page defines the term. For what it means in practice, see Conformance, certification and market access are three different things.

Who is responsible

This is the part that surprises people. A Declaration of Conformity is not issued by a laboratory. It is issued by the manufacturer or importer, on their own authority, and it is their legal responsibility if it is wrong.

Testing supports the declaration. It does not replace it, and it does not transfer the liability. A manufacturer can hold a complete test report from an accredited laboratory and still be in breach if the declaration is inaccurate, incomplete, or covers a product that differs from the one tested.

What it contains

A declaration identifies the product precisely, names the regulations and standards it is declared against, identifies the manufacturer or the authorised representative in the market, and is signed by someone with the authority to commit the company. It is kept by the manufacturer and produced on request — it is not a certificate that gets displayed.

A Declaration of Conformity is not a test report and not a certificate. The declaration is the manufacturer's own statement of responsibility, a test report is a laboratory's record of what was measured, and a certificate is a third party's attestation that a product meets a scheme's requirements. They are produced by different parties, and having one does not imply the others.