Talks about a fight between Mayweather and Mosley go back as far as 1999.
However the first serious talk of fight between the fighters came after Floyd Mayweather's win over Juan Manuel Marquez, when the two fighters confronted each other and started shoving and talking trash. However following this incident both fighters went there own way, only to meet up again.
Shane Mosley was scheduled to face Andre Berto for a WBC and WBA Welterweight title unification bout on January 30, 2010. However, the fight (and entire undercard) was called off on January 18, 2010 due to the earthquake in Haiti and Berto losing several family members in the disaster. Negotiations for a proposed matchup between Mosley and Floyd Mayweather Jr. immediately began afterwards, ending with both sides agreeing to a set date of May 1, 2010 at the MGM Grand Garden Arena in Las Vegas, Nevada. The fight is billed "Who R U Picking?"
