The objectives of this research were to provide the Illinois Department of Transportation (IDOT) with an ultrathin whitetopping (UTW) thickness design method and guidelines for UTW design, concrete material selection, and construction practices. A new mechanistic-empirical design method was proposed based on a modified version of the American Concrete Pavement Association (ACPA) design method for UTW. This proposed guide calculates the required UTW thickness based on traffic level, pavement layer geometry, climate, materials, and the pre-existing HMA condition. Laboratory testing of UTW concrete mixtures suggested many proportions and constituents can be successfully used as long as consideration is made to minimize the concrete’s drying shrinkage (e.g., limited cement content) and maintain the concrete- HMA bond. The laboratory testing coupled with previous fiber-reinforced concrete (FRC) slab tests suggested that structural fibers should be utilized in future UTW projects in order to reduce the required slab thickness without increasing the concrete strength, limit the crack width, expand the required slab size, and to extend the functional service life of fractured slabs and potentially extend the performance of non-reinforced concrete joints. A residual strength ratio was proposed to characterize the performance of any FRC mixture to be used in UTW systems. This residual strength ratio can be calculated based on measured parameters from ASTM C 1609-07 and has been incorporated into the design guide to account for the structural benefits of using FRC. Finally, recommendations for saw-cut timing and construction techniques are also presented in this report. ; published or submitted for publication ; is peer reviewed