Inter- and intraspecies cross-contaminations (CCs) of human and animal cells represent a chronic problem in cell cultures leading to false data. Microsatellite loci in the human genome harboring short tandem repeat (STR) DNA markers allow individualization of cell lines at the DNA level. Thus, fluorescence polymerase chain reaction amplification of STR loci D5S818, D13S317, D7S820, D16S539, vWA, TH01, TPOX, CSF1PO, and Amelogenin for gender determination is the gold standard for authentication of human cell lines and represents an international reference technique. The major cell banks of the USA, Germany, and Japan (ATCC, DSMZ, JCRB, and RIKEN, respectively) have built compatible STR databases to ensure the availability of STR reference profiles. Upon determination of an STR profile of a human cell line, the suspected identity can be proven by online verification of customer-made STR data sets on the homepage of the DSMZ institute. Furthermore, an additional tetraplex PCR has been established to detect mitochondrial DNA sequences of rodent cells within a human cell culture population. Since authentic cell lines are the main prerequisite for rational research and biotechnology, the next sections describe a rapid and reliable method available to students, technicians, and scientists for certifying identity and purity of human cell lines of interest.