A method for purifying an adeno-associated virus, which method comprises: 1) applying a sample of impure virus to an affinity matrix under conditions to bind the adeno-associated virus to the matrix, wherein the affinity matrix comprises an affinant capable of competing with heparan sulphate for binding to the virus; 2) eluting contaminants from the matrix to produce a virus-rich matrix; 3) eluting virus from the virus-rich matrix; 4) treating the eluted virus with a protease incapable of digesting intact virus to digest any proteinaceous contaminants; and 5) separating intact virus from the digested proteinaceous contaminants.