Overview. This chapter introduces the concept of an internet intermediary and situates their activities within the layered, modular network architecture of the internet. The services considered in this work take many forms, ranging from operators of network equipment to administrators of bulletin boards. Not all providers of internet services are properly described as ‘intermediaries’ as such, and are not necessarily to be treated comparably. Services may consist of different activities or contribute in different ways to wrongdoing. Some entities supply many distinct services which vary in their complexity, control, mental state, and degree of passivity. This makes it crucial to describe these activities accurately and with precision. As Arnold J has explained in the context of blocking injunctions, when considering questions of intermediary liability ‘it is important to consider the nature of the infringing act and its relationship with the service in question’.