Abstract The procedures used today for oligo-DNA synthesis are reviewed. The main applications of oligonucleotides in biological studies, the protecting group chemistry, the coupling procedures, and the methods for isolating and characterizing products are described. Contents . Introduction. Uses of DNA Oligomers. Established methods of synthesis and general strategies. Types of solid supports. Protection of the nucleic bases. Thymidine. Deoxycytidine. Deoxyadenosine. Deoxyguanosine . Protection of the deoxyribose. Phosphorylation and phosphitylation. The coupling step. The final deprotection step. Purification methods in DNA synthesis. Characterization of oligonucleotides. Conclusion. References.