A Postage Stamp, a small paper with pictures and other information printed on it, is primarily used as an evidence of pre-paying a fee for postal services. This also has become a collectors item and the stamp collecting has attracted several millions world over including kings and queens. The stamp collecting is some times called as the 'king of hobbies and the hobby of kings'.

• First postage stamp was issued by Great Britain in 1840, as a part of reforms in postal system based on a proposal by Rowland Hill.
• The first stamp was bearing the profile of the head of queen Victoria. As the face value of the stamp was 1 penny and black in colour, its was popularly called as Penny Black.
• In US the first stamps were issued on 1st of July 1947 in New York City. Two stamps with face values of 5-cents and 10-cents respectively were issued in that occasion. 5- cent stamp, in red brown colour depicted Benjamin Franklin, the first postmaster general of the US, and the other stamp was printed with a picture of George Washington.

As the interest in stamp collecting grew and the field expanded to cover various aspects of postage stamps, the collectors started studying stamps in details. Value of a stamp depends of its rarity. Therefore, collectors try to find something that differentiates their collection from others. A stamp can vary in many ways from another. These variations can make a stamp different from another similar looking stamp. Collectors' study normally includes the following aspects of a stamp to find differences:

• Colour
• Paper
• Water Marks
• Perforations
• Printing Process

When a particular stamp is used for long period of time it has to be reprinted several times. This can lead to variations in stamps. Generally the variations occur in the above-mentioned aspects of the Stamp.

A Stamp issued by British Guiana in 1856, known as British Guiana 1¢ magenta is one of the most rare stamps in the world. Only one specimen of this stamp is said to exist now. In 1980 it was sold at $935,000.

Treskilling Yellow is a stamp with a rare error. This was issued by Sweden in 1855. This stamp with a face value of 3 skilling had been erroneously printed in yellowish orange colour, instead of blue-green colour. In 1990 this stamp was sold for over 1 million US dollars, and in 1996 it went for 2.5 million Swiss Francs. At that time it was the most valuable stamp in the world.

US Postal Service issued a stamp now known by the name Benjamin Franklin Z-Grill in 1868. This consisted of a feature called Z-grill, a pattern embossed on the backside of the stamp, to improve the ability of the stamp to absorb the canceling ink. It is believed that there are only two specimens existing now. Currently the value of the stamp is estimated at US $ 3 million.

At times errors can occur in stamps due to faults either in design or printing. Sometimes these errors are detected after they were released for sale, and few of these stamps get into the hands of collectors. Stamps with errors are generally scarcer, and become more valuable than the perfect specimens.

Some notable stamps with errors

Inverted Jenny: Inverted Jenny is a stamp issued by US in 1918. The stamp consists of an image of an airplane named Curtiss JN-4. Due to a prinitng error, the image had been printed upside down. In 2005 this stamp was sold in an auction for US$ 525,000.

CIA Invert: Another US stamp with error known as CIA invert was issued in 1979, and one of the sheets had the handle holder, printed in black, inverted in relation to the yellow, red and white colour portions representing the flame and background for the flame. The stamp is valued at US $ 15,000.