Abstract: Providing tailored supplemental content to a user in a Network Address Translation (NAT) environment is described. Network traffic from a user to a supplemental content provider is monitored within a first network and a supplemental content identifier (ID) is identified in the monitored traffic and linked to a profile of the device or user of the device. A supplemental content provider on a second network receives a request for supplemental content that includes the supplemental content ID and uses the received supplemental content ID to retrieve the profile linked to the supplemental content ID. Supplemental content may then be generated or retrieved based on the retrieved profile and returned to the user device.