As stated on its blackout page: The Internet Archive believes that it is critical to protest and raise awareness of pending legislation in the United States: House Bill 3261, the Stop Online Piracy Act (SOPA) and S.968, the PROTECT IP Act (PIPA).
We are going dark from 6am to 6pm PST on Wednesday, January 18 (14:00 - 02:00 UTC) to drive a message to Washington. We need your help to do this.
Legislation such as this directly affects libraries (pdf) such as the Internet Archive, which collects, preserves, and offers access to cultural materials. Furthermore, these laws can negatively affect the ecosystem of web publishing that led to the emergence of the Internet Archive.
For United States residents, please take action.
For non-US Residents: Sorry for dragging you into this, and if you are willing please sign a petition to the State Department to express your concern.