Time elapsed between the time of death and discovery of the corpse is known as postmortem interval (PMI) or time since death. PMI estimation is an important but challenging issue in the forensic sciences. Time since death estimation methods rely on measuring the effect of various processes occurring in the body after decease. Over the years, several approaches for PMI estimation have been developed. Traditional methods are based on physiological, metabolic processes, physicochemical, and entomological processes to estimate the degradation of a body. Several methods have been proposed over the last 80 years for PMI determination by chemical means, leading to the emergence of a field known as “thanatochemistry”. As a result, indicators of biochemical processes, or “biomarkers,” have been proposed to estimate PMI periods. However, the biomarkers proposed from the study of thanatochemistry have been shown to be largely affected by aspects related to the environment, geographic location, cause of death, etc., limiting their accuracy and application. Nonetheless, advances in molecular biology have opened a new field (thanatobiology) for the discovery of new and more accurate biomarkers for PMI estimation.