This chapter investigates cracking, delamination, and fatigue in advanced electronic packaging, driven by 2.5D/3D integration, hybrid bonding, wafer- and panel-level packaging, chip stacking, and heterogeneous integration. These innovations introduce significant reliability challenges, in terms of thermal and mechanical stresses. The chapter examines stress singularities at material interfaces and corners using analytical and numerical methods to predict cracking and delamination. Fracture mechanics-based approaches, including interface stress analysis and delamination criteria, are discussed. Finite element analysis (FEA) is employed to assess thermal and mechanical stresses at critical interfaces. Thermal fatigue, a key reliability concern, is analyzed under power cycling, temperature cycling, and thermal shock, with factors such as preload, dwell time, and ramp rates examined. Design optimizations for wafer-level packaging (WLP), including fan-in and fan-out technologies, are discussed in detail to enhance solder ball reliability. Acceleration models for lead-free solder joint reliability based on experimental data are examined. The chapter also addresses package performance under impact loading, focusing on drop-induced failures and modeling techniques. Experimental validations and simulations highlight key influences on system-level reliability, including component placement, size, and drop orientation.