Possible Theories of Cold Fusion.

We review some of the key facts in the phenomenology of Pd-hydrides 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 tomacroscopic quantum-mechanical effects belong to the class of possible theories of those phenomena.