The present survey aims to focus on the delimitation of some definitive findings. The simple choice of terminology is charged with consequences on the conceptual level: "agreements on the forum", "clauses derogating from jurisdiction" or "agreements on the extension of jurisdiction" ? While when we talk about agreements on jurisdiction we have in mind especially the phenomenon in its civil and commercial declension, in the sense in which these expressions are traditionally used in international instruments as we see in a comparative manner with our research. The second part of the present work is based on a theoretical and jurisprudential discourse that seeks, at a monographic level, to introduce the central theme of our investigation: How the burden of proof is actually distributed in common law systems? We have decided to deal with all the theoretical aspects of the question, including the matter of presumptions which, as we know, is a topic that can conceptually be traced back to that interests us, given that the main effect of the application of a presumptive rule is to altering the natural allocation of probative costs. The concrete conduct in our paragraphs will be specifically dedicated to a case study of the distribution of the burden of proof as implemented by the American jurisprudence.