The Long-Term Pavement Performance (LTPP) database includes deflection basins measured on thousands of test sections across the United States. These deflection data were used to backcalculate the elastic layer modulus of both flexible and rigid pavements. This report documents the tools, data analyses, backcalculation and forward calculation packages, and procedures used to calculate the in-place elastic layer modulus of the LTPP test sections. It summarizes the backcalculated elastic layered modulus of both new and rehabilitated flexible and rigid pavements in the LTPP program and demonstrates their use in day-to-day practice for pavement design, rehabilitation, and management. Many agencies have used the LTPP deflection data for calibrating mechanistic-empirical distress transfer functions, including those in the Mechanistic-Empirical Pavement Design Guide.