Secondary liability, or indirect infringement, arises when a party materially contributes to, facilitates, induces, or is otherwise responsible for directly infringing acts carried out by another party. The US has statutorily codified secondary liability rules for trademarks and patents, but for matters relating to copyright, this has solely been a product of case law developments. In other words, courts, rather than Congress, have been the primary developers of theories and policies concerning secondary liability.