This chapter provides an in-depth and comprehensive investigation of warpage in semiconductor packaging and its critical impact on manufacturability, reliability, and thermal performance. Advanced technologies such as 2.5D/3D integration, hybrid bonding, wafer- and panel-level packaging, chip stacking, fan-out, package-on-package (PoP), and system-in-package (SiP) have made warpage a pivotal challenge, affecting not only manufacturability but also electrical, thermal, and long-term reliability performance. This chapter explores state-of-the-art measurement techniques, including shadow moiré and digital image correlation (DIC). The mechanics of warpage is further discussed, starting with fundamental concepts of stress–strain relationships and temperature-dependent material properties, then progressing to viscoelastic models. Process-dependent properties, curing kinetics, and effective curing shrinkage are discussed in detail. Advanced models are introduced to address curing-dependent material characteristics, temperature-dependent stress–strain relations, and viscoelastic effects. These models are implemented in finite element analysis (FEA) for precise warpage prediction and mitigation. The chapter also provides a comprehensive review of warpage mitigation strategies, including UV curing processes, innovative manufacturing approaches, capped-die designs for achieving warpage-free packaging, and the use of liquid metals as thermal interface materials.