A tracker module for use in a peer-to-peer communications network, the tracker module configured to manage content data transfers between a discrete set of network elements forming a tracker domain within the network, the tracker module comprising: a storage medium having a content table stored therein, the content table including a record of content data available to each network element within the tracker domain; a communications interface for receiving a content data request from a requesting network element in the tracker domain; a processing unit for interrogating the content table stored in the storage medium and determining whether the requested content data is available to any of the network elements within the tracker domain; wherein the tracker module is configured so that: if the requested content data is available to any of the network elements within the tracker domain, the processing unit determines a list of network elements through which the content data is available, and the communications interface sends said list to the requesting network element; and the tracker module characterized by being configured so that if the requested content data is not available to any of the network elements within the tracker domain, the communications interface sends a supplementary request for the content data to another tracker module in the network, the other tracker module being higher up in a tracker hierarchy in the network. a storage medium having a content table stored therein, the content table including a record of content data available to each network element within the tracker domain; a communications interface for receiving a content data request from a requesting network element in the tracker domain; a processing unit for interrogating the content table stored in the storage medium and determining whether the requested content data is available to any of the network elements within the tracker domain; wherein the tracker module is configured so that: if the requested content data is available to any of the network elements within the tracker domain, the processing unit determines a list of network elements through which the content data is available, and the communications interface sends said list to the requesting network element; and the tracker module characterized by being configured so that if the requested content data is not available to any of the network elements within the tracker domain, the communications interface sends a supplementary request for the content data to another tracker module in the network, the other tracker module being higher up in a tracker hierarchy in the network. if the requested content data is available to any of the network elements within the tracker domain, the processing unit determines a list of network elements through which the content data is available, and the communications interface sends said list to the requesting network element; and the tracker module characterized by being configured so that if the requested content data is not available to any of the network elements within the tracker domain, the communications interface sends a supplementary request for the content data to another tracker module in the network, the other tracker module being higher up in a tracker hierarchy in the network.