Internet blocking, also known as Internet filtering or content control, is the use of hardware or software to restrict access to undesirable online content. Blocking is distinct from monitoring, which tracks online behavior without preventing access, although both functions are often found together in software applications. Filtering of pornographic and political material receives the most attention, but violent online videos and video games, cyberbullying threats, images of violent behavior, and hate group websites can also be blocked. This entry describes Internet blocking technology and examines its efficiency, prevalence, and social impacts.