A/RES/55/199 order to reflect their experiences and the lessons learned and to provide ideas and proposals for the way forward for the further implementation of Agenda 21 in relevant areas; 12. Encourages effective contributions from, and the active participation of, all major groups, as identified in Agenda 21, at all stages of the preparatory process, in accordance with the rules and procedures of the Commission on Sustainable Development, as well as its established practices related to the participation and engagement of major groups; 13. Decides that the Commission on Sustainable Development at its tenth session shall meet as an open-ended Preparatory Committee that will provide for the full and effective participation of all States Members of the United Nations and members of the specialized agencies, as well as other participants in the Commission on Sustainable Development, in accordance with the rules of procedure of the functional commissions of the Economic and Social Council and the supplementary arrangements established for the Commission on Sustainable Development by the Council in its decisions 1993/215 of 12 February 1993 and 1995/201 of 8 February 1995; 14. Invites regional groups to nominate their candidates for the Bureau of the tenth session of the Commission on Sustainable Development by the end of 2000 so that they can be involved in its preparations in advance of the first session of the Preparatory Committee; 15. should: Decides that the Commission, acting as the Preparatory Committee, (a) Undertake the comprehensive review and assessment of the implementation of Agenda 21 and the other results of the Conference on the basis of the results of national assessments and subregional and regional preparatory meetings, the documentation to be prepared by the Secretary-General in collaboration with the task managers, and other inputs from relevant international organizations, as well as on the basis of contributions from major groups; (b) Identify major accomplishments implementation of Agenda 21; and lessons learned in the (c) Identify major constraints hindering the implementation of Agenda 21, propose specific time-bound measures to be taken and institutional and financial requirements, and identify the sources of such support; (d) Address new challenges and opportunities that have emerged since the Conference, within the framework of Agenda 21; (e) Address ways of strengthening the institutional framework for sustainable development and evaluate and define the role and programme of work of the Commission on Sustainable Development; (f) Consider and decide on accreditation for the participation in the preparatory process and the Summit of relevant non-governmental organizations that are not in consultative status with the Economic and Social Council; (g) Propose a provisional agenda and possible main themes for the Summit based on the results of the preparatory activities carried out at the national, subregional, regional and international levels, taking into account also the input of major groups; 4