http://wikimediafoundation.org/wiki/English_Wikipedia_anti-SOPA_blackout
Today, the Wikipedia community announced its decision to black out the English-language Wikipedia for 24 hours, worldwide, beginning at 05:00 UTC on Wednesday, January 18 (you can read statement from the Wikimedia Foundation here). The blackout is a protest against proposed legislation in the United States —the Stop Online Piracy Act (SOPA) in the U.S. House of Representatives, and the PROTECTIP Act (PIPA) in the U.S. Senate— that, if passed, would seriously damage the free and open Internet, including Wikipedia.
This will be the first time the English Wikipedia has ever staged a public protest of this nature, and it’s a decision that wasn’t lightly made. Here’s how it’s been described by the three Wikipedia administrators who formally facilitated the community’s discussion.