This chapter examines defamation cases arising from traditional media sites and user-generated media entries. It first provides an overview of the tort of defamation, and the issue of who is responsible and potentially liable for an online defamatory statement. It then looks at the Defamation Act 2013, considering when defences may be raised to a claim in defamation, and how online publication and republication may result in defamation. Four cases are analysed: Dow Jones v Gutnick, Loutchansky v Times Newspapers, King v Lewis, and Jameel v Dow Jones. The chapter explores intermediary liability, particularly the liability of UK internet service providers, by citing recent decisions on intermediary liability such as Tamiz v Google, Delfi v Estonia, and MTE v Hungary, as well as specific intermediary defences found in the Defamation Act 2013. The chapter concludes by discussing key social media cases such as McAlpine v Bercow and Monroe v Hopkins.