A Unifying Completeness Theorem in Quantified Modal logic Giovanna Corsi Abstract: A general strategy for proving completeness theorems for quantified modal logics is provided. Starting from free quantified modal logic K, with or without identity, extensions obtained either by adding the principle of universal instantiation or the converse of the Barcan formula or the Barcan formula are considered and proved complete in a uniform way. Completeness theorems are also shown for systems with the extended Barcan rule as well as for some quantified extensions of the propositional modal logic B. The incompleteness of Q'.B+BF is proved too.