Almost a million species of insects are known. Insects are defined by having six legs and a body divided into three segments: head, thorax and abdomen. Chitin is an organic material that makes up the exoskeleton of insects. There are three life cycles of insects, ametabolous or incomplete and paurometabolous or gradual and homotabulous or complete metamorphosis. These life cycles are important in insect aging to aid in forensic investigations (Houck and Siegel. Entomology). Forensic entomology is the study of insects to aid in legal or criminal investigations. The primary reason for studying the presence and life stages of inserts on a decomposing body is to establish the postmortem interval, or PMI. Insects can not only be used to determine a PMI, but they can also help investigators when it comes to actually solving the crime in question. Forensic entomology can be divided into three areas: medicolegal, urban, and stored product pests. Urban entomology involves insects affecting homes, buildings, and other human-based environments. Stored pest entomology involves insects infesting stored goods such as food and clothing. In this article forensic entomology will be the focus as it is the type of entomology that entomologists use to use insects to solve criminal cases, (Houck and Siegel. Entomology). Estimation of a PMI: It has been found that the decomposition process is best divided into five phases: fresh phase, swollen phase, decay phase, post-decay phase, and remains. The new phase begins the moment the individual dies and lasts until swelling is observed. The bloated stage usually occurs within two to seven days of death. At this stage rot begins and the gases produced by the bacteria cause... middle of paper... an argument made to prevent the jury from hearing the entomological evidence. It is important to understand the practice of entomology and how it relates to criminal cases. The entomologist must have a background in legal practices and in his scientific discipline (Esf.edu). Conclusion: The main reason for studying forensic entomology is to establish the time since death. Recognizing each species and its life stages, as well as knowing how long an insect lasts in a particular life stage, is the basis for establishing a PMI. The use of forensic entomology is a growing area of ​​research, which will become more widespread as more research is completed on the topic. This is important in criminal cases as it provides a time frame in which the crime occurred so that it is possible to narrow down each suspect's options or acquit the defendant.