To track a U.S. post office package, enter the assigned tracking number into the special search tool at the USPS website, which provides updates on the status of the package. Some tracking numbers may have to be purchased separately, depending on the method of shipping.
Some forms of USPS mail, such as First-Class, require an additional fee for a tracking number, while others, such as Priority Mail, include a tracking number with the purchase price. The format of this number varies depending on the method of shipping. The USPS also affixes an internal tracking number to each parcel, though this number cannot be used for customer tracking.