In addition to individualization through DNA profiling, the identification and detection of body fluids linked to a crime, such as blood, saliva, vaginal secretions, epithelium, and semen, make the particular evidence highly significant, forensically relevant, and helpful in correlating incidents with those implicated in a given crime. Most forensic labs currently employ methods for body fluid identification based on immunological and enzymatic testing. The forensic evidence, which is typically recovered in trace amounts, is partially consumed by the current technologies. Consequently, it becomes challenging to profile DNA from the same trace evidence and identify body fluids using multiple techniques for body fluid identification. That being said, messenger RNA (mRNA) markers can help with the screening and identification of many body fluids in a single step, as they are transcripts specific to a given tissue. In different stages of the extraction process, RNA and DNA can be extracted simultaneously from the same biological trace sample. Hence, body fluid identification using mRNA markers along with individualization by DNA profiling from the same trace evidence is possible, which provides a highly significant and forensically relevant evidence to correlate specific people to crimes. This chapter provides an extensive review and discussion on mRNA profiling as a valuable tool for the identification of forensically relevant body fluids in solving crime cases.