The search for life on other planets has also provided impetus for further study of psychrophilic, or cold-loving, bacteria on earth. The review by Deming (pp 301–309) describes recent progress in understanding the physiology of bacteria that inhabit such environments as Antarctic frozen lakes. These studies also have earthly interest. Industries are finding increasing applications for enzymes that are active at cold temperatures, and psychrophiles are an obvious source of these biocatalysts. Thus, microbial ecology continues to expand its boundaries, into the inner depths of soil particles on Earth and beyond our planet in the quest for life outside Earth’s boundaries.