Daniel A. Portnoy is a microbiologist and immunologist who studies the cellular and molecular mechanisms of host–pathogen interactions. He is best known for groundbreaking research on Listeria monocytogenes, which revealed how intracellular pathogens invade, replicate, and evade immune defenses. His lab pioneered genetic and molecular approaches to study innate immunity, including the discovery of pathways that activate host cell defenses against bacterial infection. Portnoy’s work has had major implications for understanding bacterial pathogenesis, inflammation, and the development of vaccines and therapeutics. His research integrates microbial genetics, immunology, and cell biology to dissect how pathogens subvert host processes. Portnoy is a Professor of Plant & Microbial Biology and Molecular & Cell Biology at UC Berkeley. He is a member of the National Academy of Sciences, National Academy of Inventors and a Fellow of the American Academy of Microbiology. His research has been published in Science, Nature, and Cell. He has received awards such as the NIH MERIT Award and has trained numerous graduate students and postdocs who lead labs around the world. His expertise spans microbiology, immunology, and host–pathogen interactions.