This review describes synthetic pathways to mono-, di- and oligonucleotides modified in the phosphate group(s) by substitution of one or several oxygen atoms with sulfur. The known sulfur-modified phosphate groups are nucleoside 3′- and 5′-O-phosphorothioates, nucleoside thiodi- and triphosphates, nucleoside cyclic phosphorothioates, di- and oligonucleosideO,O-phosphorothioates, nucleoside 3′-S-phosphorothioates, nucleoside and oligonucleoside 5′-S-phosphorothioates, nucleosideO-phosphorodithioates, di- and oligonucleosideO,O-phosphorodithioates, di- and oligonucleosideO,S-phosphorodithioates, thiophosphortriesters, thiophosphoramidates, and methylphosphonothioates.