The gallbladder is a small organ located below the liver. It's function is to store bile used by the intestines to digest food.
Gallstones - small calcified deposits - sometimes form and block the bile ducts which lead from the gallbladder to the intestines.
In many cases, the problem becomes so severe, that the only effective treatment is to remove the entire gallbladder. This is the most common reason for gallbladder surgery. Other reasons for removing the gallbladder include chronic or severe or the growth of a tumor.