Sherwood, RobertThe Internet is a collection of shared resources. Internet users share bandwidth and processing resources both in the network at routers and on the network's edge at servers. However, the Internet's architecture does not prevent nodes from consuming disproportionate resources. In practice, resource exhaustion does occur due to inefficiently scaling systems, selfish resource consumption, and malicious attack. The current Internet architecture has limited support for both securing and identifying shared Internet resources. This dissertation has two main contributions. First, I demonstrate the existence of end-host protocols that protect the availability of shared Internet resources. I consider resource sharing with respect to cooperative, selfish, and malicious user models, and for each case design a protocol that protects resource availability without modifying the existing Internet infrastructure. Second, I design and validate measurement techniques for discovering shared Internet resources including links and routers. Specifically, I improve the completeness and accuracy of resource maps by combining embedding probes, disjunctive logic programming, and information from the record route IP option. We validate and quantify the improvement of our maps by comparison to publicly available research networksen-USDissertationComputer Science