An intrauterine device (IUD or coil)[1] is a small contraceptive device, often 'T'-shaped, often containing either copper or levonorgestrel, which is inserted into the uterus. They are one form of long-acting reversible contraception which are the most effective types of reversible birth control.[2] Failure rates with the copper IUD is about 0.8% while the levonorgestrel IUD has a failure rate of 0.2% in the first year of use.[3] Among types of birth control they, along with birth control implants, result in the greatest satisfaction among users.[4] As of 2007, IUDs are the most widely used form of reversible contraception, with more than 180 million users worldwide.[5]