Today, Valentine's Day is indeed a well celebrated day in the whole world where love fills the air -- flowers & gifts all around. When did it all start and who started Valentine's Day?

History of Valentine's Day from Wikipedia (Read the whole content here)

Valentine's Day or Saint Valentine's Day is a holiday celebrated on February 14 by many people throughout the world. In the English-speaking countries, it is the traditional day on which lovers express their love for each other by sending Valentine's cards, presenting flowers or offering confectionery. The holiday is named after two among the numerous Early Christian martyrs named Valentine. The day became associated with romantic love in the circle of Geoffrey Chaucer in the High Middle Ages, when the tradition of courtly love  flourished.

The day is most closely associated with the mutual exchange of love notes in the form of "valentines". Modern Valentine symbols include the heart-shaped outline, doves, and the figure of the winged Cupid. Since the 19th century, handwritten notes have largely given way to mass-produced greeting cards. The sending of Valentines was a fashion in nineteenth-century Great Britain, and, in 1847, Esther Howland developed a successful business in her Worcester, Massachusetts home with hand-made Valentine cards based on British models. The popularity of Valentine cards in 19th century America, where many Valentine cards are now general greeting cards rather than declarations of love, was a harbinger of the future commercialization of holidays in the United States. It's considered one of the Hallmark holidays.

The U.S. Greeting Card Association estimates that approximately one billion valentines are sent each year worldwide, making the day the second largest card-sending holiday of the year, behind Christmas. The association estimates that, in the US, men spend on average twice as much money as women.