On the occasion of the 25th anniversary of the United Nations Register of Conventional Arms, the Office for Disarmament Affairs is publishing this special edition of the Disarmament Study Series. This volume contains a newly written overview of the Register for reference by governments and the interested public, original material to guide national points of contact in preparing and submitting reports for the Register, and the report of the 2016 Group of Governmental Experts on the continuing operation of the Register. The United Nations Register of Conventional Arms is an annual reporting mechanism through which governments can share information on weapons they transferred the previous year. Member States reporting to it provide information on the build-up and volume of the conventional arsenals which it deems essential to maintain a credible defence and perform effective peacekeeping tasks.