ICANN/U.S. Government Contract for Performance of the IANA Function (Aug. 14, 2006) (full-text).
This contract, originally dated February 2, 2000 and amended or replaced multiple times, is a no-cost, sole-source contract between ICANN and the U.S. government authorizing ICANN to perform the largely technical functions that were previously performed by IANA. These functions involve administrative tasks such as allocating IP address blocks, editing the root zone file, and coordinating the assignment of unique IP numbers.
However, without this contract, ICANN would not have the ability to coordinate the Internet's identifier systems. Under the contract, any changes in the root zone file must be audited and approved by the U.S. Department of Commerce.