During the course of an infection, a pathogenic bacterium has to sense the environment and adjust its gene expression appropriately. One such environmental cue is the difference in temperature inside and outside the host. RNA thermosensors are structures that can respond to differences in temperature by altering their conformation and thereby allowing/preventing binding of the ribosome to the translational start site. This chapter discusses different types of RNA thermosensors in general and RNA thermosensors known to control virulence gene expression in particular.