We celebrate it each year, but what's the background story - I was really surprised.
The day gets its name from a famous saint. There are a few stories of who he was.
The popular belief about St Valentine is that he was a priest from Rome, he died on the 14th February 269 AD.
Emperor Claudius II had banned marriage because he thought married men were bad soldiers. Valentine felt this was unfair, so he broke the rules and arranged marriages in secret.
When Claudius found out, Valentine was thrown in jail and sentenced to death.
He then fell in love with the jailer's daughter and when he was taken to be killed on 14 February he sent her a love letter signed "from your Valentine". The rest as they say is history.
It's amazing how stories keep rolling down through the years and become an influence on society. The first known Valentines Day celebration was recorded in 496 AD. The first hand written Valentines message in English was in 1477 - Nearly 1,000 years later and things were just going.
These days literally billions of pounds are spent between couples exchanging gifts, expressing their undying love for one another - it's become one of the most commercialised days of the year.
For a full overview of St. Valentine take a look at this.
Happy Valentines Day.