Thiocarbonyl compounds (thioamides, thioesters, thioketones...) react readily with a large variety of reagents (nucleophiles, electrophiles and radicals) due to their weak C=S bond and the aptitude of sulfur to stabilise an adjacent charge or radical centre. Thus, nucleophilic additions, deprotonation, and sigmatropic rearrangements are often more facile than in the oxygen series. Moreover, a number of specific reactions have been uncovered: thiophilic addition of nucleophiles, Michael addition of enethiolates, the Eschenmoser reaction, oxidation to sulfines, a large variety of [4+2] and [3+2] cycloaddition reactions with 1,3-dienes and 1,3-dipoles. Far from being purely exotic species, thiocarbonyl compounds are now efficient and specific tools and have indeed been used in multi-step synthetic schemes leading to various products of biological interest.