The transfer of genetic material (e.g., plasmid) in a site- and strand-specific manner between a donor and recipient (e.g., bacterial) cells through direct contact.

Bacterial conjugation is where DNA is transferred between cells by direct cell-to-cell contact through a pilus (a small hair-like tube structure) between two cells. In many cases, the transferred plasmid confers the recipient bacterium some genetic advantage such as genes for antibiotic resistance. Conjugation is an important mechanism for transfer of drug resistance genes.