Abstract: Sulfonated and oxidized indene polymers obtainable by(a) polymerization of indene or indene derivatives of the general formula I ##STR1## where R.sup.1 is hydrogen, methyl or ethyl and n is 1 or 2, or of mixtures which contain the compounds I as well as other copolymerizable and/or non-polymerizable organic compounds in an amount of at least 10% by weight,b) sulfonation of the polymer with a sulfonating agent at from 40.degree. to 130.degree. C., andc) non-chain-degrading oxidation of the polymer at from 80.degree. to 180.degree. C.These indene polymers are suitable for use as dispersants for example in dye and pigment preparations.