Achieving restoration goals by applying conventional remediation approaches has been difficult at many contaminated sites. For example, remediation of groundwater to a condition allowing for unlimited use and unrestricted exposure remains a significant challenge at some sites. A variety of existing approaches could be applied at these challenging sites; however, guidance describing the elements, tools, and options for successful remediation at complex sites is needed. Success at complex sites may ultimately depend on being able to integrate multiple remediation approaches, risk management strategies, and long-term monitoring and management. This project will produce a guidance document that provides a technical foundation for predictive analyses, for progressive remedy implementation, and for defining and achieving a successful remediation strategy at complex sites. Case studies will be included to help define complex sites. This document, along with an associated Internet- based training course, will help regulators and site managers develop protective approaches that have a strong scientific and technical foundation.