Membrane-bound desaturases play key role in metabolism of polyunsaturated fatty acids. Characterization of these enzymes and their genes is the first step in basic understanding of their proper functioning in living cells as well as in tailor-made preparation of highly-specific and highly-productive strains of microorganisms interesting for applied biotechnology. It is also the crucial step in creation of transgenic agricultural crops with enhanced content of individual polyunsaturated fatty acids. Properties and applications of identified membrane-bound desaturases genes and enzymes are discussed in this review.