Exchange of information: confidentiality and restricted use for tax administration, with limited exceptions for trade secrets and public policy. Article 27 mandates exchange of information necessary for tax administration and enforcement, requiring secrecy and restricting disclosure to authorities concerned with assessment, collection, enforcement, prosecution, appeals or oversight, while permitting judicial disclosure. Limits preserve domestic laws and administrative practices and protect trade secrets and public policy, yet obligate States to use information gathering measures even without a domestic interest and not to refuse requests solely because information is held by financial intermediaries or concerns ownership interests.