Exposure to extremes of temperatures cause stresses which are sometimes lethal to living cells. Microorganisms in nature, however, are extremely diverse and some of them can live happily in the freezing cold of Antarctica. Among the cold adapted psychrotrophs and psychrophiles, the psychrotrophic bacteria are the predominant forms in the continental Antarctica. In spite of living in permanently cold area, the antarctic bacteria exhibit, similar to mesophiles, ‘cold-shock' response albeit at a much lower temperatures, e.g., at 0–5°C. However, because of permanently cold condition and the long isolation of the continent, the microorganisms have acquired new adaptive features in the membranes, enzymes and macromolecular synthesis. Only recently these adaptive modifications are coming into light due to the efforts of various laboratories around the world. However, a lot more is known about adaptive response to low temperature in mesophilic bacteria than in antarctic bacteria. Combined knowledge from the two systems is providing useful clues to the understanding of basic biology of low temperature growing organisms. This article will provide an overview of this area of research with a special reference to sensing of temperature and regulation of gene expression at lower temperature.