Heterogeneous integration is a methodological approach and a research field focused on the assembly and packaging of dissimilar materials, components, or functional subsystems into a single, higher-level system or package. This concept investigates the techniques and challenges associated with combining elements fabricated using different processes, materials, or technologies, such as diverse semiconductor types, passive components, or sensors, to achieve enhanced overall system performance, functionality, and efficiency that may not be attainable through monolithic integration alone. Its significance lies in enabling the creation of complex, high-performance electronic and photonic systems by leveraging the optimal technology for each constituent part.