Wikipedia plans to take its English-language site offline on Wednesday as part of protests against proposed anti-piracy laws in the US.
The user-generated news site Reddit and the blog Boing Boing have also said they will take part in the "blackout".
The sites' webmasters are opposed to the Stop Online Piracy Act (SOPA) and Protect Intellectual Property Act (PIPA) being debated by Congress.
However, Twitter has declined to take part in the shutdown.
Marco Werman talks with Zeynep Tufekci, assistant professor at the school of information at the University of North Carolina, Chapel Hill.