Summary. -We review some of the key facts in the phenomenology of Pdhydrides usually referred to as «cold fusion». We conclude that all theoretical attempts that concentrate only on few-body interactions, both electromagnetic and nuclear, are probably insufficient to explain such phenomena. On the other hand we find good indications that theories describing collective, coherent interactions among elementary constituents leading to macroscopic quantum-mechanical effects belong to the class of possible theories of those phenomena.PACS 12.20.Ds -Specific calculations and limits of quantum electrodynamics.PACS 52.55.Pi -Confinement in fusion experiments (including α-particle effects, scaling laws, etc.).Introduction.