Exchange of information requires authorities to obtain and share tax relevant data while preserving confidentiality protections. Article 26 obliges competent authorities to exchange foreseeably relevant information, including documents, for applying the Convention and administering or enforcing domestic tax laws; recipients must treat such information as secret and use it only for assessment, collection, enforcement, prosecution, appeals or oversight, except where both States' laws permit other uses and the supplying State authorizes them. States need not act contrary to their laws, supply unobtainable information, or disclose trade or professional secrets or information contrary to public policy, but must use their information gathering measures to obtain requested information even absent a domestic interest, including information held by banks or fiduciaries.