Vectors are carriers of DNA which are used to transfer gene of interest into host cell. Vectors used at present, are engineered in such a way that help easy linking of foreign DNA and selection of recombinants and non recombinants. Plasmids and bacteriophages have ability to replicate within the bacterial cells independent of the control of chromosomal DNA. Ti plasmid is used vector for plant cell and retrovirus is used as a vector for animal cell.