The majority of the Earths biosphere is cold and exposed to temperatures below 5°C throughout the year. Having evolved special mechanisms to overcome the life-endangering influence of low temperatures, psychrophiles, i.e. cold-adapted microorganisms, have successfully colonized these environments. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, and these adaptations render cold-adapted organisms particularly useful for biotechnological applications. This book presents the most recent knowledge of (i) boundary conditions for microbial life in the cold, (ii) microbial diversity in various cold ecosystems, (iii) molecular cold adaptation mechanisms and (iv) the resulting biotechnological perspectives.