The biggest change in postage stamps since their introduction in 1840 is the price.
The First Stamp
The Penny Black, the first postage stamp, was introduced in Great Britain in 1840. As you might guess, it cost a penny. Prior to stamps, postage was paid by the recipient.
Stamps in the U.S.
In 1847, two stamps were issues in the U.S. One was a 5-cent stamp (for a letter going fewer than 300 miles), and the second was a 10-cent stamp (distance greater than 300 miles).
In 1855, it became a requirement to pay postage in advance, that is, by the sender. Prepaid postcards, costing a penny, came on the scene in 1871.
Stamps were printed in large, uncut sheets prior to 1857 in the U.S. Individual stamps were removed with scissors.
In 1863, the price difference for distance was eliminated, and the U.S. rate was 3 cents. In 1883, the price became 2 cents. The rate went back to 3 cents during World War I, became permanent in 1932, and stayed until 1958.
Postage rates went to 42 cents in May 2008, and will rise to 44 cents in May 2009.