Quality and reliability aspects of 3D IC and packages are discussed in this chapter. The main focuses are interconnects-related quality and reliability issues. For the 3D packages, interconnects may include microbump, TSV, UBM, copper traces, etc. We compare them to the quality and reliability concerns observed in the existing interconnects, as well as the methodology to predict the field performances. We shall cover microstructure changes and failures driven by mechanical stressing, electromigration (EM), and thermomigration (TM). This way we can see how the transition, for example, from C-4 joints to microbumps may affect the failure modes. On mechanical stressing, we emphasize the brittle nature as well as microvoid formation, especially Kirkendall void formation in microbumps. A string of voids in a brittle material can easily lead to fracture damage. The interest in mechanical failures is because for mobile and wearable devices, the frequency of impact and dropping to the ground is high. On EM and TM in microbumps and TSV, we emphasize the enhanced failure mode due to Joule heating.