Throughout the history of forensic medicine, the postmortem interval (PMI) has been one of the commonly and thoroughly investigated problems. Despite many decades of research, accuracy in estimation of the time of death has not significantly improved and no single method can be reliably used to accurately estimate the time of death. PMI estimation can be classified based on evidence into corporal evidence, environmental evidence and anamnestic evidence. Nowadays for estimation of PMI, temperature-based methods, thanatochemistry, thanatology, molecular methods, microbial assays, optical coherence tomography, virtual autopsy, radionuclide-based methods, entomology, histopathology and immunohistochemistry are used. It is expected that future research will result in improved techniques with enhanced accuracy in the estimation of PMI, which will benefit both human and veterinary investigations.