Exchange of information: tax authorities may obtain and share confidential taxpayer data for tax administration, subject to legal limits. Article 26 mandates exchange of information between Contracting States' competent authorities for tax administration and enforcement, including documents, and requires such information to be treated as secret and used only by authorised persons for tax assessment, collection, enforcement, prosecution, appeals or oversight, except where both States' laws and the supplying State permit other uses. It sets limits: no obligation to act contrary to domestic law or supply unobtainable information or trade secrets, while requiring use of information gathering measures even absent domestic interest and prohibiting refusal solely because information is held by banks or fiduciaries. Provisions permit on site interviews and presence during tax examinations with consent and notification.