Theories and physics-based modeling are the basis for numerical simulation of sintering for predicting how complex powder compacts densify and shrink under thermal and mechanical driving forces. Because sintering involves phenomena from atoms to bulk parts, multiscale methods are integrated: molecular dynamics captures atomic diffusion; discrete element, Monte Carlo, and phase-field techniques resolve mesoscale particle rearrangement and grain growth; and finite-element or finite-difference schemes forecast macroscopic, multiple physical phenomena involved in sintering, such as heat transfer and mechanics. Rigorous validation of each model and verification of each solver safeguard predictive accuracy. By replacing costly trial-and-error tests, this computational framework accelerates scientific understanding and technological progress in sintering.