Exchange of information: treaty obligation to obtain and share tax relevant data while maintaining confidentiality and use limits. Article 26 creates an obligation for contracting states to exchange information foreseeably relevant to applying the Convention or administering and enforcing domestic tax laws, including documents or certified copies, and to use information gathering measures to obtain requested information even if not needed for the requested State's own tax purposes. Information received must be kept secret and used only for specified tax assessment, collection, enforcement, prosecution, appeals, or oversight purposes unless both States permit other uses and the supplying State authorises them. Limitations preserve domestic law, administrative practice, non obtainable information, trade secrets, and public policy, while preventing refusal solely because information is held by financial intermediaries or concerns ownership interests.