The Clustered regularly interspaced short palindromic repeats (CRISPR) system represents a congenital immunity of prokaryotes which enables their defense against phages. After the phage infects the bacteria for the first time, the bacteria integrates a part of a chopped viral DNA into its CRISPR locus which enables the recognition and removal of the same phage when the next infection occurs. There are many variants of the CRISPR-Cas system and the most frequently used one is the CRISPR-Cas9. CRISPR-Cas9 has piqued many scientists interest as a genetic modification tool. It is composed of two components; single guided RNA (sgRNA) and endonuclease Cas9 (CRISPR associated 9). SgRNA leads the endonuclease Cas9 to its complementary sequence where the sequence chops double stranded DNA. The target DNA location is complementary with sgRNA. SgRNA nucleotide sequence programming facilitates the modification of many genes. Genetic modification through CRISPR-Cas9 sytem is based on the breakdown induction of double stranded DNA, which is mediated by nuclease Cas9 which then repairs itself with the DNA repairing system non-homologous end joining (NHEJ) and homology-directed repair (HDR). NHEJ is error-prone system, which leads to accumulation of insertions and deletions in the repaired DNA region. A template of DNA is needed for HDR and is then inserted in the region that has been broken down. CRISPR-Cas9 can be used for insertion, deletion and correction of the targeted gene. The clinical use of the CRISPR-Cas system could enable the treatment of genetic diseases such as Duchenne muscular atrophy, spinal muscular atrophy, sickle cell anemia and other diseases that currently have very few therapeutic options. Precise, specific and quick genetic modifications interceded by the CRISPR-Cas system are innovative therapeutic options of the near future and could be used for the treatment of inheritable and other diseases caused by genome disturbance.