Tomorrow, (Wednesday, January 18), Wikipedia and several other sites will go dark. They are protesting two “anti-piracy” acts that are threats to the open sharing of information. Here are a few sources that might be useful in understanding this issue:
ABC News: Wikipedia Blackout: Websites Wikipedia, Reddit, Others Go Dark Wednesday to Protest SOPA, PIPA
PC World: Wikipedia, Other Sites to Protest Anti-Piracy Bills with Blackouts
American Library Association: PIPA, SOPA and OPEN Act Quick Reference Guide
A video from Public Knowledge: