Antisense technology has advanced substantially in the past few decades and now is a wellestablished therapeutic approach in medicinal chemistry, and it may prove to be a valuable tool in the treatment of a wide range of diseases. Phosphorothioate oligonucleotides are among the most important and promising antisense agents. However, the key drawback lies in their polydiastereomerism, which manifests itself in the different chemical and biological properties of the diastereomeric species. Methodologies towards the stereocontrolled synthesis of antisense phosphorothioate oligonucleotides have been well investigated in recent years. In this review, the progress in this field is summarized.