The in-depth reviews of national communications (NCs) are conducted by an international team of experts, coordinated by the UNFCCC secretariat. The review of each NC typically involves a desk-based study and an in-country visit, and aims to provide a comprehensive, technical assessment of a Party's implementation of its commitments. The in-depth review results in an in-depth review report, which typically expands on and updates the NC. The in-depth review reports aim to facilitate the work of the COP in assessing the implementation of commitments by Annex I Parties. The reports also allow easier comparison of information between NCs of Parties, although no common indicators are employed.

As outlined in annex II of decision 2/CP.17, the IAR process includes a technical review of BRs, where relevant, in conjunction with the annual GHG inventories, and NCs of developed country Parties, which will result in an individual review report for each developed country Party. When the BRs are submitted in the same year as the NCs, the reviews are conducted in conjunction, in-country. When BRs are not submitted in the same year as the NCs, the reviews are conducted through centralized reviews. The technical reviews are conducted by an international team of experts from Annex I and non-Annex I Parties, selected from the Roster of Experts.