Two-dimensional van der Waals (vdW) materials are layered crystalline solids characterized by their bonding anisotropy, in which the atoms within each monolayer are connected by strong covalent bonds, while the layers are bound by significantly weaker and directionless van der Waals forces in the through-plane direction. The latter feature allows the atomically thin monolayers of these 2D materials to be isolated and recombined without lattice matching, without commensurability, and with any member of the 2D vdW materials family. This allows us to generate a virtually limitless library of designer solids from these monolayers assembled in any arbitrary sequence and orientation. The customizability of the vertical composition and structure of the overall solid at the atomic limit translates to novel vibrational properties, thereby opening up new opportunities for exploring thermal transport phenomena at the nanoscale. My dissertation will focus on engineering novel thermal transport properties in artificial solids assembled from large-area, polycrystalline 2D vdW materials. Firstly, I will discuss the effect of interlayer rotation on the thermal anisotropy of stacked film assembled from transition metal dichalcogenide (such as MoS2) monolayers. Our film has a unique rotationally scrambled structure—large crystalline domains in plane, but complete crystalline mismatch in the through-plane direction between atoms from adjacent monolayers—that imbues our material with record-breaking thermal conductivity anisotropy. We reveal new insights on the thermal transport mechanisms in our films and explain them using collaborative-effort atomistic simulations. In this dissertation, I will also characterize the contribution of air-solid interfacial thermal transport in the measurement of the apparent thermal conductance of suspended vdW monolayers. My dissertation will propose several new directions, enabled by this research, for further engineering of thermal transport in 2D vdW crystals. This work paves the way for creating novel materials solutions for improved thermal management in nanoelectronics and provides a new playground for studying exotic thermal physics at the nanoscale.