Internet intermediaries play a central role in modern commerce and society. Although their economic and social importance is well-recognised, their legal liability remains poorly understood, and, until now, no work has specifically addressed their legal responsibility for wrongdoing carried out by third parties using their facilities or platforms. This work fills that gap by providing comprehensive coverage of the legal duties owed by intermediaries and the increasingly complex schemes that regulate their activities. The first part of the work introduces the concept of an internet intermediary, general doctrines of primary and secondary liability, and the European enforcement regime. The second part examines the liability of intermediaries in specific areas of law, with a detailed analysis of the applicable liability rules, and the major English case law, and decisions of the Court of Justice that interpret and apply them. The final part of the work provides guidance on remedies and limitations. Written by an expert author from the intellectual property chambers at 8 New Square, Lincoln's Inn, this is an essential guide for lawyers advising on liability, privacy, and online regulation.