Great strides have been made in recent years to improve pavement design and construction in practice. Highway agencies have begun implementing the mechanistic-empirical pavement design guide (MEPDG) for pavement design and performance-related specifications for pavement construction. Despite the progress made toward designing and constructing durable and long lasting pavements, not nearly enough attention has been made to the role of pavement foundations (i.e., subbase and subgrade layers) in pavement design, construction, and performance. The four papers in this dissertation present results of studies that assessed different quality control (QC) and quality assurance (QA) methods for constructing stabilized pavement foundations, compared in situ stiffness properties of stabilized pavement foundations, assessed the influence of pavement foundation stiffness on roller-integrated compaction monitoring (RICM) measurements during asphalt pavement construction, and compared the performance of asphalt pavements that had been constructed with pavement foundations using recycled materials. In addition to the four papers, the dissertation provides an overview of the handling of pavement foundation design and construction in current pavement design guides. Key findings from this research indicated that strength- and stiffness-based in situ tests are better suited for pavement foundation construction QC/QA than conventional density-based methods; stiffness of the subgrade governs pavement foundation overall stiffness during thaw-weakening; RICM measurements taken during asphalt pavement construction are sensitive to pavement foundation stiffness; and pavement foundations using recycled materials can yield better performing yet still cost effective asphalt pavements.