The rapid growth of communication environments such as the Internet has spurred the development of a wide range of systems and applications based on peer-to-peer ideologies. As these applications continue to evolve, there is an increasing effort towards improving their overall performance. This effort has led to the incorporation of measurement-based adaptivity mechanisms and network awareness into peer-to-peer applications, which can greatly increase peer-to-peer performance and dependability. Unfortunately, these mechanisms are often vulnerable to attack, making the entire solution less suitable for real-world deployment. In this dissertation, we study how to create robust systems components for adaptivity, network awareness, and responding to identified threats. These components can form the basis for creating efficient, high-performance, and resilient peer-to-peer systems.