From Wikipedia:
The first Christmas cards were commissioned by Sir Henry Cole and illustrated by John Callcott Horsley in London on the 1st of May 1843. The central picture showed three generations of a family raising a toast to the card's recipient: on either side were scenes of charity, with food and clothing being given to the poor. Allegedly the image of the family drinking wine together proved controversial, but the idea was shrewd. Two batches totaling 2,050 cards were printed and sold that year for a shilling each.
Early English cards rarely showed winter or religious themes, instead favoring flowers, fairies and other fanciful designs that reminded the recipient of the approach of spring. Humorous and sentimental images of children and animals were popular, as were increasingly elaborate shapes, decorations and materials. In 1875 At Christmas 1873, a firm producing lithographs began creating greeting cards for the popular market in England and began selling the Christmas card in America in 1874, thus the first time a printer offered cards in America. The owner of that printer, Louis Prang, is sometimes called the "father of the American Christmas card." The popularity of his cards led to imitations that eventually drove him from the market. The advent of the postcard spelled the end for elaborate Victorian-style cards, but by the 1920s, cards with envelopes had returned.
In the early 1930s, the use of color printing appeared, a move that would propel the U.S. greeting card industry toward continued growth and expansion.
During World War II, the industry rallied for the war effort, providing cards for the soldiers overseas. This period also marked the beginning of its close relationship with the U.S. Postal Service.
By the 1950s, the studio card – a long card with a short punch line – appeared on the scene to firmly establish the popularity of humor in American greeting cards.
During the 1980s, alternative cards began to appear – cards not made for a particular holiday or event, but as a more casual reminder of our connections to one another. The popularity of “non-occasion" cards continues to swell.
Explosive growth in electronic technology, and burgeoning consumer use of the Internet, gave birth to the electronic greeting card or E-card in the late 1990s. The development of this entirely new medium for card-sending served to further expand the industry, producing new E-card publishers as well as E-greeting product offerings by traditional publishers.
(source:www.greetingcard.org)