Genomic engineering is widely used in studying gene function, designing diseases models, biopharmaceutical research, drug discovery and many other applications. CRISPR (Clustered Regulatory Interspaced Short Palindromic Repeats)/Cas9 systems is a newly developed yet the most popular method for genome editing. Besides the basic employment of gene knock-out, CRISPR/Cas9 system can be applied to selective gene activation and repression, purification of specific genomic DNA and fluorescent protein-tagging in live cells through modifications of the Cas9.