To begin the festival, members of the Luperci, an order of Roman priests, would gather at the sacred cave where the infants Romulus and Remus, the founders of Rome, were believed to have been cared for by a she-wolf or lupa. The priests would then sacrifice a goat, for fertility, and a dog, for purification.

The boys then sliced the goat's hide into strips, dipped them in the sacrificial blood and took to the streets, gently slapping both women and fields of crops with the goathide strips. Far from being fearful, Roman women welcomed being touched with the hides because it was believed the strips would make them more fertile in the coming year. Later in the day, according to legend, all the young women in the city would place their names in a big urn. The city's bachelors would then each choose a name out of the urn and become paired for the year with his chosen woman. These matches often ended in marriage. Pope Gelasius declared February 14 St. Valentine's Day around 498 A.D. The Roman 'lottery' system for romantic pairing was deemed un-Christian and outlawed. Later, during the Middle Ages, it was commonly believed in France and England that February 14 was the beginning of birds' mating season, which added to the idea that the middle of February — Valentine's Day — should be a day for romance. The oldest known valentine still in existence today was a poem written by Charles, Duke of Orleans to his wife while he was imprisoned in the Tower of London following his capture at the Battle of Agincourt. The greeting, which was written in 1415, is part of the manuscript collection of the British Library in London, England. Several years later, it is believed that King Henry V hired a writer named John Lydgate to compose a valentine note to Catherine of Valois.

In Great Britain, Valentine's Day began to be popularly celebrated around the seventeenth century. By the middle of the eighteenth century, it was common for friends and lovers in all social classes to exchange small tokens of affection or handwritten notes. By the end of the century, printed cards began to replace written letters due to improvements in printing technology. Ready-made cards were an easy way for people to express their emotions in a time when direct expression of one's feelings was discouraged. Cheaper postage rates also contributed to an increase in the popularity of sending Valentine's Day greetings. Americans probably began exchanging hand-made valentines in the early 1700s. In the 1840s, Esther A. Howland began to sell the first mass-produced valentines in America.

According to the Greeting Card Association, an estimated one billion valentine cards are sent each year, making Valentine's Day the second largest card-sending holiday of the year. (An estimated 2.6 billion cards are sent for Christmas.)

Approximately 85 percent of all valentines are purchased by women. In addition to the United States, Valentine's Day is celebrated in Canada, Mexico, the United Kingdom, France, and Australia.

Valentine greetings were popular as far back as the Middle Ages (written Valentine's didn't begin to appear until after 1400), and the oldest known Valentine card is on display at the British Museum. The first commercial Valentine's Day greeting cards produced in the U.S. were created in the 1840s by Esther A. Howland. Howland, known as the Mother of the Valentine, made elaborate creations with real lace, ribbons and colorful pictures known as "scrap".