Under the Convention, all Parties must report on the steps they are taking to implement the Convention (Articles 4.1 and 12). Each Annex I Party must submit its initial report, known as a "national communication", within six months of the entry into force of the Convention for that Party.

The majority of Annex I Parties submitted their first national communications in 1994 or 1995 and their second in 1997, except for most Parties with economies in transition, who submitted their second communications in 1998 (COP 2 decided to grant these countries a longer timeframe to prepare their communications).

Since 1996, Annex I Parties have also been required to submit an annual greenhouse gas inventory, beginning with data for their base year (in most cases 1990), and up to the last but one year prior to the year of submission.

In preparing their national communications and inventories, Annex I Parties must follow reporting guidelines. The reporting guidelines used for the first national communications were revised at COP 2 for the preparation of the second round of communications, and revised again at COP 5 for the third round. At COP 5, Parties also adopted guidelines for reporting on global climate observing systems.

Starting in 2000, Annex I Parties must now use a common reporting format, also adopted at COP 5, for preparing their annual inventory data.

The Convention states that the information provided by Annex I Parties is to be reviewed by the COP (Article 4.2(b)). In-depth reviews of the first and second national communications of Annex I Parties, including inventory data, have taken place based on procedures established by COP 1. As part of the review process, the secretariat has prepared compilation and synthesis documents of national communications.

At COP 5, Parties adopted separate guidelines for the technical review of greenhouse gas inventories by Annex I Parties. These will be used during a two-year trial period, beginning in 2000.

The in-depth review of each national communication results in the publication of an in-depth review report, which covers each major section of the national communication. The in-depth review reports expand on, and complement, the information already given and provide more up-to-date information which has become available since the publication of the national communication. 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 the national communications of Parties, although no common indicators are employed.

Important developments regarding Annex I Party national communications took place at COP 5, when revised reporting guidelines, including a common reporting format for inventory data and reporting guidelines on global climate observing systems, were adopted (see "background" above).

At part I of SBI 13 (Lyon, Sept), Parties considered a compilation prepared by the secretariat of the latest available annual inventory data submitted by Annex I Parties. They did not adopt any substantive conclusions, but requested the secretariat to further elaborate the information contained in that compilation in the form of graphs and tables for the next meeting of the SBI in The Hague in November.

Parties will continue their discussions on the latest available annual inventory data at part 2 of SBI 13 in The Hague, with a view to recommending a draft decision to COP 6.

At SBI 14 (May/June 2001), Parties will continue their discussions, initiated at SBI 12, on whether detailed guidelines for the in-depth review of national communications should be developed.

Possible revisions to the common reporting format for greenhouse gas inventories will be considered at SBSTA 15 (Oct/Nov, 2001), with a view to recommending a decision to COP 7.

The third national communications of Annex I Parties are due in November 2001 and will also be subject to in-depth review.