Horizontal gene transfer is a process where genetic material is transferred between organisms in a manner other than traditional reproduction. This can occur between different species, allowing for the sharing of traits such as antibiotic resistance or metabolic capabilities. It plays a significant role in the evolution of bacteria and other microorganisms. There are several mechanisms of horizontal gene transfer, including transformation, where bacteria take up free DNA from their environment, transduction, which involves viruses transferring DNA between bacteria, and conjugation, where two bacteria connect and exchange genetic material. This process contributes to genetic diversity and adaptation in various organisms.