They are often revered as the two clubs in world football who most footballers would love to play for if the chance arose. For most professionals, the opportunity of donning the famous red and blue of Barcelona or white of Real Madrid is often too good to turn down.
Giants of the European game and boasting an impressive 18 European Cups between them, it's easy to see why players are so keen on getting themselves a deal with either of the Spanish behemoths.
The focus on the pair has been even greater in the last decade, thanks, in part, to the back and forth rivalry and quite ridiculous goalscoring exploits of both Lionel Messi and Cristiano Ronaldo. Both those players have become synonymous with their respective club and will go down as legends when all is said and done.
However, unlike 'CR7' and 'Leo', some players have opted to represent both Madrid and Barca during their playing careers, with some even choosing to make the direct switch from Nou Camp to Bernabeu, or vice-versa.
It takes a special player to be given a chance by both Real and Barca, but these men can boast of that very feat...