Exchange of information requires competent authorities to share tax relevant data subject to confidentiality and defined limits. Article 27 requires competent authorities to exchange foreseeably relevant tax information, including documents, for applying the Convention and administering domestic tax laws; such information must be treated as secret and disclosed only to officials concerned with assessment, collection, enforcement, prosecution, appeals, or oversight and used solely for those purposes, subject to the supplying State authorising any broader use. States are not obliged to act contrary to their laws, to supply unobtainable information, or to disclose trade secrets or information against public policy; information must nevertheless be obtainable using normal information gathering measures and cannot be refused solely because it is held by banks, nominees, or fiduciaries.