Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.

Conjugation is a mechanism of horizontal gene transfer, as are transformation and transduction, though these two other mechanisms do not involve cell-to-cell contact.

Bacterial conjugation was discovered by Nobel Prize winners Joshua Lederberg and Edward Tatum. They showed that the bacterium Escherichia coli entered a sexual phase during which it could share genetic information.