Heterogeneous integration combines dies from different process technologies, materials, or functions into a single package, enabling system-level optimization beyond monolithic scaling. Approaches: (1) 2.5D—dies side-by-side on silicon interposer with through-silicon vias (TSVs) and fine-pitch redistribution; (2) 3D stacking—dies stacked vertically with TSVs or hybrid bonding; (3) Fan-out—dies embedded in reconstituted wafer with RDL interconnects; (4) Chiplet architecture—modular die connected via high-bandwidth interface; (5) System-in-Package (SiP)—multiple die in single package with substrate routing. Technology enablers: (1) Advanced bonding—hybrid bonding (Cu-Cu direct bond at sub-2μm pitch), micro-bumps, TCB; (2) TSVs—vertical connections through silicon (5-10 μm diameter); (3) Fine-pitch RDL—2/2 μm L/S redistribution layers; (4) Bridge interconnects—embedded silicon bridges (Intel EMIB). Applications: (1) HPC—logic + HBM memory stacking; (2) AI accelerators—compute chiplets + memory + I/O die; (3) 5G—RF + digital + power management; (4) Automotive—sensor fusion, ADAS processors. Benefits: combine best-node logic with mature-node analog/I/O, higher yield (smaller die), faster time-to-market, design flexibility. Challenges: thermal management (stacked die heat dissipation), testing (known-good-die requirement), design tools (multi-die co-design), supply chain complexity. Industry direction: TSMC CoWoS/InFO, Intel Foveros/EMIB, Samsung I-Cube. Heterogeneous integration is the primary scaling vector as Moore's Law monolithic scaling becomes increasingly difficult and expensive.