RNA thermometers (RNATs) are cis-encoded regulatory elements that modulate transla‐ tional efficiently in response to environmental temperature. Since their initial discovery, numerous RNATs have been identified and characterized, with the majority of currently known RNATs present in a wide variety of bacterial species. RNATs repress translation at relatively low temperatures by physically preventing binding of the ribosome to the regulated transcript by incorporating the Shine-Dalgarno sequences (and/or start codon) into an inhibitory structure. As the environmental temperature increases, the inhibitory structure within the RNAT is destabilized and the repression of translation initiation is gradually relieved. With the development of identification techniques, the rate at which RNATs are identified, and the understanding of the molecular mechanisms governing their regulator function, has grown exponentially. With the ever-increasing number of characterized RNATs, broad families of these regulators have now been identified. It has also become abundantly clear that RNATs influence several essential physiological proc‐ esses. This chapter aims to summarize the current knowledge of bacterial RNATs, with special emphasis placed on the molecular mechanisms underlying RNAT function, exper‐ imental techniques used to identify and characterize RNATs, families of bacterial RNATs, as well as biological processes controlled by RNATs, and future directions of the field.