Today, criminals have recognized the paramount importance of physical evidences like: fingerprint, footprint, blood and etc. Thus, they try to leave the crime scene without a trace. In contrast to the abovementioned evidences, fibers are so tiny and criminals either don’t see or have no time to destroy them. These evidences (in addition to their diversity in color and material) can help the C.S.I officers in discovering crimes like: murder, rape, violent crimes, burglary and so forth. In this article, the necessity of fibers examination in criminal researches, fibers classification, searching the crime scene to find fibers and sending them to labs, comparative methods to identify fibers and their criminal importance will be discussed.