This study examines the state of the practice of quality assurance (QA) related to critical structural materials and components: those for which failure poses a threat to public safety or to the integrity of the transportation system (e.g., bridge girders, bridge columns, and sign/ signal/luminaire supports). The study focuses on conventional structural materials (e.g., steel, concrete, wood, and aluminum), which comprise the vast majority of highway structures in use or in the planning and design stages. Brief coverage of some newer materials in the highway infrastructure, such as fiber-reinforced polymers, high-performance concrete, and high-performance steel, is provided.   The intent of the report is to discuss problems (both perceived and real) that arise from insufficient or potentially inappropriate QA practices, indicate potential opportunities for improvement to practices through additional or revised practices, and discuss the state of the practice with respect to how most agencies currently are operating.  The report for this topic can be purchased at https://gulliver.trb.org/bookstore/