Cas9, derived from the bacteria Streptococcus pyogenes, is a key component of the CRISPR-Cas9 gene-editing system. It is an RNA-guided DNA endonuclease that can be programmed to target and cut specific DNA sequences within the genome. The Cas9 protein, along with a single-guide RNA (sgRNA), forms a complex that recognizes a specific sequence of DNA preceding a short sequence known as a PAM (protospacer adjacent motif) and introduces a double-strand break at that location. This ability allows for precise gene editing through mechanisms such as non-homologous end joining (NHEJ) or homology-directed repair (HDR), enabling researchers to knockout genes, insert new genetic material, or make specific changes to the DNA sequence. Cas9's high specificity and programmability have made it a powerful tool in fields ranging from basic research to potential therapeutic applications in treating genetic disorders and cancer. Recent advancements have also focused on improving the precision and reducing off-target effects of Cas9, making it a safer and more efficient tool for gene editing.