Philately, or stamp collecting, has been around for generations as a hobby. In fact, it started as soon as stamps first came into existence. Ever since nations began regulating and standardizing the post, enthusiasts have shown more interest in these little paper squares. While stamps may seem ordinary, some are expensive, especially the vintage and rare ones. Here are some of the most valuable stamps in the world that are one of a kind.

British Guiana 1c Magenta, 1856
The British Guiana 1c Magenta is today’s most valuable rare stamp, priced at about $9.48 million. It has traded hands across the world multiple times since its creation.

Treskilling Yellow, 1855
The Treskilling Yellow stamp resulted from a color error when printing one of Sweden’s first stamps. Its value stands at about $2.6 million today.

The Sicilian Error of Color, 1859
The Sicilian Error of Color, 1859, which features the side profile of a bearded man, is so well-preserved that it looks as if it was printed just yesterday. The $2.6 million stamp was initially released in yellow but misprinted in stark blue.

Baden 9 Kreuzer Error, 1851
Priced at about $1.3 million, the Baden 9 Kreuzer Error is one of the first stamps issued by the former German state of Baden.

The Inverted Jenny, 1918
At a value of $1.35 million, this stamp features one of the Jenny biplanes first used by the US Post Office to carry mail but with the plane accidentally printed upside down.

1c Benjamin Franklin Z Grill, 1868
This stamp has a value of about $935,000. It was sold at an auction for the said price in 1998.

3c George Washington w/ B Grill, 1867
At about $900,000, this stamp is relatively affordable than the others on this list. The George Washington B Grill features a waffle-like pattern used to identify fraud.

Tiflis Stamp, 1857
Also known as the Tiflis Unique, the $700,000 Tiflis stamp features a metallic sheet and embossed lettering, resembling a metal bookplate.

24c Declaration of Independence, 1869
At about $625,000, the 24c Declaration of Independence stamp has a highly detailed, two-toned rendering of John Trumbull’s famous painting of the presentation of the Declaration of Independence to the Continental Congress.

Hawaiian Missionaries, 1851
Hawaiian Missionaries were the first stamps issued by the Kingdom of Hawaii. Its rarity has driven its price to about $600,000 today.