Isocyanates are usually produced from amines by phosgenation, i.e. treating with phosgene:
These reactions proceed via the intermediacy of a carbamoyl chloride ().  Owing to the hazardous nature of phosgene, the production of isocyanates requires special precautions.  A laboratory-safe variation masks the phosgene as oxalyl chloride.  
Another route to isocyanates entails addition of isocyanic acid to alkenes.  Complementarily, alkyl isocyanates form by displacement reactions involving alkyl halides and alkali metal cyanates.
Three rearrangement reactions involving nitrenes give isocyanates:
* Schmidt reaction, a reaction where a carboxylic acid is treated with ammonia and hydrazoic acid yielding an isocyanate.
* Curtius rearrangement degradation of an acyl azide to an isocyanate and nitrogen gas.
* Lossen rearrangement, the conversion of a hydroxamic acid to an isocyanate via the formation of an O-acyl, sulfonyl, or phosphoryl intermediate.