Inter partes review is a way to challenge the validity of an issued US patent based on prior art patents or printed publications. This type of review became available in 2012, replacing a previous process called inter partes reexamination. Inter partes review is considered a cheaper alternative to district court patent litigation in some cases because the review is conducted by the USPTO. When a patent holder asserts a claim against an alleged infringer, the alleged infringer will commonly initiate inter partes review to present prior art arguments against the patent holder.