The specification of the materials and methods used in earthworks and foundations for highways, railways, and airfield runways can be approached in several ways. There is a need for a more sustainable use of resources, and specifications that make best possible use of material properties are required. A performance-based approach is considered the best way to achieve this. The functional requirements of a performance-based specification for UK highway foundations were considered. The recently researched performance-based specification, demonstrating the steps to its development, determination of the engineering requirements, suitable target values, and potential construction-related implications, is explained. Performance-based specifications offer the advantage of better incorporation of the principles that underpin sustainable construction and require a fuller understanding of material behavior for their development and implementation. However, contractual issues and implications for construction need to be considered carefully to allow a full performance-based approach to be adopted successfully. In the United Kingdom, a staged implementation of a performance specification is needed to gain experience in both the process and the field measurement methods, some of which are relatively novel, and to reduce the risk of contractual disputes or potential failures and thus a negative reaction from the industry.