In many cases there is lack of consensus between the countries about the extent of aquifers or even their transboundary character. The First Assessment revealed many such examples. Different positions between countries regarding the transboundary character of an aquifer, its real extent or its hydraulic connection to surface water systems also emerged in the preparations of the Second Assessment. It is a positive development that, since the First Assessment, Bosnia and Herzegovina and Serbia have acceded to the Convention and that the former Yugoslav Republic of Macedonia is preparing for accession.