Isocyanates are electrophiles, and as such they are reactive toward a variety of nucleophiles including alcohols, amines, and even water having a higher reactivity compared to structurally analogous isothiocyanates.
Upon treatment with an alcohol, an isocyanate forms a urethane linkage:
where R and R' are alkyl or aryl groups.
If a diisocyanate is treated with a compound containing two or more hydroxyl groups, such as a diol or a polyol, polymer chains are formed, which are known as polyurethanes.
Isocyanates react with water to form carbon dioxide:
This reaction is exploited in tandem with the production of polyurethane to give polyurethane foams.  The carbon dioxide functions as a blowing agent.
Isocyanates also react with amines to give ureas:
The addition of an isocyanate to a urea gives a biuret:
Reaction between a di-isocyanate and a compound containing two or more amine groups produces long polymer chains known as polyureas.
Carbodiimides are produced by the decarboxylation of alkyl and aryl isocyanate using phosphine oxides as a catalyst: