A Christmas card is a greeting card sent as part of the traditional celebration of Christmas in order to convey between people a range of sentiments related to Christmastide and the holiday season. Christmas cards are usually exchanged during the weeks preceding Christmas Day by many people (including some non-Christians) in Western society and in Asia. The traditional greeting reads "wishing you a Merry Christmas and a Happy New Year". There are innumerable variations on this greeting, many cards expressing more religious sentiment, or containing a poem, prayer, Christmas song lyrics or Biblical verse; others focus on the general holiday season with an all-inclusive "Season's greetings". The first modern Christmas card was by John Calcott Horsley.

A Christmas card is generally commercially designed and purchased for the occasion. The content of the design might relate directly to the Christmas narrative with depictions of the Nativity of Jesus, or have Christian symbols such as the Star of Bethlehem or a white dove representing both the Holy Spirit and Peace. Many Christmas cards show Christmas traditions, such as seasonal figures (e.g., Santa Claus, snowmen, and reindeer), objects associated with Christmas such as candles, holly, baubles, and Christmas trees, and Christmastime activities such as shopping, caroling, and partying, or other aspects of the season such as the snow and wildlife of the northern winter. Some secular cards depict nostalgic scenes of the past such as crinolined shoppers in 19th-century streetscapes; others are humorous, particularly in depicting the antics of Santa and his elves.

The first known Christmas card was sent by Michael Maier to James I of England and his son Henry Frederick, Prince of Wales in 1611. It was discovered in 1979 by Adam McLean in the Scottish Record Office. It was hand-made and incorporated Rosicrucian imagery, with the words of the greeting – "A greeting on the birthday of the Sacred King, to the most worshipful and energetic lord and most eminent James, King of Great Britain and Ireland, and Defender of the true faith, with a gesture of joyful celebration of the Birthday of the Lord, in most joyand fortune, we enter into the new auspicious year 1612" – being laid out to form a rose.

The first commercially available card was commissioned by Sir Henry Cole and designed by John Callcott Horsley in London 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: Cole had helped introduce the Penny Post three years earlier. Two batches totaling 2,050 cards were printed and sold that year for a shilling each.

Early British 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. At Christmas 1873, the lithograph firm Prang and Mayer began creating greeting cards for the popular market in Britain. The firm began selling the Christmas card in America in 1874, thus becoming the first printer to offer cards in America. Its owner, Louis Prang, is sometimes called the "father of the American Christmas card." By the 1880s, Prang was producing over five million cards a year by using the chromolithography process of printmaking. However, the popularity of his cards led to cheap 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. The extensive Laura Seddon Greeting Card Collection from the Manchester Metropolitan University gathers 32,000 Victorian and Edwardian greeting cards, printed by the major publishers of the day, including Britain's first commercially produced Christmas card.

The production of Christmas cards was, throughout the 20th century, a profitable business for many stationery manufacturers, with the design of cards continually evolving with changing tastes and printing techniques. The now widely recognized brand Hallmark Cards was established in 1913 by Joyce Hall with the help of brother Rollie Hall to market their self-produced Christmas cards. The Hall brothers capitalized on a growing desire for more personalized greeting cards, and reached critical success when the outbreak of World War I increased demand for cards to send to soldiers. The World Wars brought cards with patriotic themes. Idiosyncratic "studio cards" with cartoon illustrations and sometimes risque humor caught on in the 1950s. Nostalgic, sentimental, and religious images have continued in popularity, and, in the 21st century, reproductions of Victorian and Edwardian cards are easy to obtain. Modern Christmas cards can be bought individually but are also sold in packs of the same or varied designs. In recent decades changes in technology may be responsible for the decline of the Christmas card. The estimated number of cards received by American households dropped from 29 in 1987 to 20 in 2004. Email and telephones allow for more frequent contact and are easier for generations raised without handwritten letters – especially given the availability of websites offering free email Christmas cards. Despite the decline, 1.9 billion cards were sent in the U.S. in 2005 alone. Some card manufacturers now provide E-cards. In the UK, Christmas cards account for almost half of the volume of greeting card sales, with over 668.9 million Christmas cards sold in the 2008 festive period. In mostly non-religious countries (e.g. Czech Republic), the cards are called New Year Cards; they are sent before Christmas and the emphasis (design, texts) is mostly given to the New Year, omitting religious symbols.

"Official" Christmas cards began with Queen Victoria in the 1840s. The British royal family's cards are generally portraits reflecting significant personal events of the year.

There is a long-standing custom for the American President and First Lady to send White House Christmas Cards each holiday season. The practice originated with President Calvin Coolidge, who was the first president to issue a written statement of peaceful tidings during the holidays in 1927. President Herbert Hoover was the first to give Christmas notes to the White House staff, and President Franklin Delano Roosevelt was the first president to utilize the card format (rather than the previously used notes or a written statement) that most closely resembles the Christmas cards of today.