SOPA is currently snaking its way through the US House of Representatives. The impending PROTECT IP Act is also under scrutiny.
The enormous free encyclopedia site will be out for 24 hours.
SOPA is a bill that threatens directly enforced action against sites that host user-uploaded content which may have been copy-righted. The bill threatens to facilitate a U.S.-intelligence-led crackdown on information flow by providing legal barricades to slow and/or stop the flow of information on high-traffic sites. Anonymous posted a video reply back in November here.
Wikipedia released a statement saying today's blackout was made "through a consensus decision-making process." It quoted from a recent statement from administrators that indicates that the decision to go dark was "the largest level of participation in a community discussion ever seen on Wikipedia."