Three-dimensional integration (3D-I) of multiple layers of active devices into a single chip is opening up opportunities for disruptive microelectronic, optoelectronic, and microelectromechanical systems. Integrated circuit (IC) designers are driving 3D-I for new products, which in turn is providing opportunities in process technology and modeling. This article reviews the status of 3D-I and describes some research opportunities for both process engineers and modeling and simulation engineers. The opportunities discussed center around "stacking" and interconnecting multiple active and/or passive layers or strata of traditional planar designs into "hyperfunctional" 3-D systems. The focus is on electrical 3D-ICs, using BCB as the adhesive to bond wafers, and copper-based, through-silicon-vias or through-strata-vias (TSVs) for interconnection. However, much of the material applies to other approaches to 3D-I and other 3-D systems. Both recently established methods and advanced research efforts are discussed for process technology and thermomechanical modeling and simulation of Cu-based TSVs and BCB-based bonding.