This Dissertation Characterizes the Space of Trust Metrics, Under Both The Scalar Assumption Where Each Assertion Is Evaluated Independently, and The Group Assumption Where a Group of Assertions Are Evaluated In Tandem. We Present A Quantitative Framework For Evaluating the Attack Resistance of Trust Metrics,And Give Examples of Trust Metrics That Are Within a Small Factor Of Optimum Compared To Theoretical Upper Bounds. We Discuss Experiences With a Real World Deployment Of a Group Trust Metric, the Advogato Website. Finally, We Explore Possible Applications of Attack Resistant Trust Metrics, Including Using It As To Build a Distributed Name Server, Verifying Metadata In Peer-To-Peer Networks Such As Music Sharing Systems, and a Proposal For Highly Spam Resistant E-Mail Delivery.