Mardi Gras, which literally means "Fat Tuesday", is officially known as Shrove Tuesday in Europe and was a day for fun and indulgence before Ash Wednesday and weeks of fasting leading up to Easter Sunday.
In the US it originally started around 1730's by African slaves gathering and celebrating on plantations in Louisiana. It became an open celebration in 1744 in New Orleans, but almost disappeared in the early 1800's.
Modern Mardi Gras celebrations started in 1867, with the first organization or krewe established. Today there are several krewes, usually named after a mythological hero or a Greek God, responsible for organizing all the aspects of the festival including parades, parties, costume contests and political satire.
Although it is celebrated in many places, New Orleans remains the heart and soul of Mardi Gras with the throwing of the beads from floats in parades being one of the most popular traditions.