Recent advances in the development of ruthenium catalysts for the atom transfer radical addn. of polyhalogenated compds. to olefins ('Kharasch reaction') are described. Three classes of homogeneous catalysts are discussed: halfsandwich complexes with h6-arene, h5-cyclopentadienyl or h5-carborane ligands, ruthenium complexes with alkylidene- or vinylidene ligands and polynuclear complexes. Furthermore, first attempts to use immobilized ruthenium complexes as heterogeneous catalysts for the Kharasch reaction are summarized.