Plants collect, concentrate and conduct light throughout their tissues, thus enhancing light availability to their resident microbes. This review explores the role of photosensing in the biology of plant-associated bacteria and fungi, including the molecular mechanisms of red light sensing by phytochromes and blue light sensing by LOV-domain proteins in these microbes. Bacteriophytochromes function as major drivers of the global transcriptome and in the lightmediated suppression of virulence, motility and conjugation in some phytopathogens, and in the light-mediated induction of the photosynthetic apparatus in a stem-nodulating symbiont. Bacterial LOV proteins also influence light-mediated changes in both symbiotic and pathogenic phenotypes. Although red light sensing by fungal phytopathogens is poorly understood, fungal LOV proteins contribute to blue light regulation of traits including asexual development and virulence. Collectively, these studies highlight that plant microbes have evolved to exploit light cues, and that light sensing is often coupled with sensing other environmental signals.