WADP Numbering System

The WNS (for WADP Numbering System) is the worldwide numbering system for postage stamps created by the UPU and the World Association for the Development of Philately (WADP).

The WNS was launched on 1 January 2002, with the primary aim of compiling a database of all postage stamps legally issued, from that date onwards, by the issuing postal authorities of UPU member countries and territories that have signed up to the WNS.

Only those postage stamps received by the UPU International Bureau and whose authenticity has been confirmed are assigned a unique WNS number and added to the WNS website.

The WNS therefore serves as a primary reference tool for checking postage stamp issues, helping to safeguard the philatelic industry against illegal issues.

In addition, the system helps WNS member issuing authorities to build their stamp sales. Each postage stamp registered on the WNS website includes a link to the website of the member concerned, and to its online shop where available, making it easier for collectors to buy the stamps.

This makes the WNS a three-pronged system, providing:
 * Authentication – a control mechanism against illegal issues;
 * Expertise – a reference tool for philatelic stakeholders (collectors, dealers, catalogue publishers, etc.);
 * Marketing – a sales channel for designated operators.

Numbering
The WNS records all the postage stamps officially issued by a WNS member stamp issuing authority in any given year, regardless of the format (individual stamps, booklets, miniature sheets, etc.).

A postage stamp is assigned a unique authentication number based on four criteria:
 * design
 * face value or postage rate indication
 * colours
 * size
 * perforation

When any one of the above criteria differs on another postage stamp, the stamp is given a different WNS number.