Reviews are given on the preparation and properties of arylphosphorus compounds and aliphatic phosphorus compounds containing silicon; on the cleavage of the aryl-silicon bond in acid media; and on the cleavage of the benzyl-silicon bond in alkaline media. Detailed information has been obtained on the effect of a variety of phosphorus-containing nuclear substituents on the rates of cleavage of the aryl-silicon bond in concentrated sulphuric acid-glacial acetic acid, and of the benzyl-silicon bond in aqueous methanolic-sodium hydroxide solution. The substituents were found, in most cases, to be strongly electron-withdrawing and the results clearly indicate that the electrons of the benzene ring can enter the d-orbitals of phosphorus. The protonation, in strongly acidic media, of the phosphoryl-oxygen, in triphenylphosphine oxide, was studied spectrophotometrically. It is apparent that triphenylphosphine oxide does not behave as a true Hammett base. Several silicon-substituted derivatives of ethylphosphonic acid and dimethyl ethylphosphonate were prepared and the properties of these investigated, with special reference to pyrolytic and solvolytic reactions.