Catalogues split each country's stamps into categories, and knowing which kind you're holding makes identification much faster.

Definitive stamps

Everyday stamps for ordinary mail. They are printed in large numbers over many years, usually in a long series of values with one shared design, such as a monarch's portrait, a national symbol, flowers or birds.

Because of their long print runs, definitives often exist in many varieties: different papers, perforations, watermarks, printers and shades. Specialists collect these closely, and some varieties are much scarcer than the basic stamp.

Commemorative stamps

Issued for a limited time to mark an event, anniversary or person, such as the Olympics, a national holiday or a famous scientist. They are usually larger and more colourful than definitives and are sold for only a few months. Special issues without an anniversary, such as Christmas stamps or wildlife series, are similar.

Semi-postal (charity) stamps

These are sold for more than their postal value, with the extra amount going to a cause. The two amounts are often printed together, like "20+10". They are common in Europe, especially Germany (Wohlfahrtsmarken), Switzerland (Pro Juventute, Pro Patria), Belgium and the Netherlands.

Airmail stamps

Issued to pay the higher rate for sending mail by air. They are often marked "Air Mail", "Par Avion", "Luftpost" or "Correo Aéreo", and aircraft commonly appear in the design. They were most common from the 1920s to the 1970s.

Postage due stamps

Applied by the post office to underpaid mail, to show how much the recipient had to pay. They usually have simple designs with a large numeral. Look for inscriptions such as "Postage Due", "Porto", "Taxe" or "Segnatasse".

Official stamps

Used only by government departments. Some are ordinary stamps with an overprint (such as "Official", "Dienst" or "Service"), and others are separate designs.

Revenue (fiscal) stamps

Not postage stamps at all. They paid taxes and fees on documents, legal papers and goods. They are often inscribed "Revenue", "Stempelmarke" or "Timbre fiscal". Some stamps were valid for both postage and revenue ("Postage & Revenue"), and catalogues usually value fiscally used copies, often cancelled by pen, lower than postally used ones.

Other formats you'll meet

  • Souvenir sheets and miniature sheets. One or more stamps printed on a small decorated sheet.
  • Booklet panes. Stamps from booklets, often with one or two straight (imperforate) edges.
  • Coil stamps. Sold in rolls, with straight edges on two opposite sides.
  • Self-adhesive stamps. Peel-off stamps, common since the 1990s, often with wavy die-cut edges instead of perforations.

Knowing the type narrows your catalogue search. Then identify the exact variety by its perforation and watermark.