Exchange of information requirement mandates cross border tax data sharing with strict confidentiality and limited legal exceptions. Exchange obligations require competent authorities to share foreseeably relevant information, including documents, for administering or enforcing domestic tax laws; such information must be treated as secret and disclosed only to authorized persons for tax assessment, enforcement, appeals or oversight, except where laws of both States and the supplying State permit other uses. A State need not take measures contrary to its laws, supply information not obtainable under its law, or disclose trade secrets or information against public policy; however, it must use its information gathering measures to obtain requested information even if it lacks a domestic interest, and bank or fiduciary holding does not alone justify refusal.