The effect of DNA or nucleotides on the photophysical properties of metal polypyridyl complexes (especially those of ruthenium, osmium, rhodium, rhenium and copper) is reviewed. On binding to DNA the excited states of certain complexes show reduced non-radiative decay and protection from oxygen or water, while in other cases the excited state is quenched because of electron transfer from the nucleobases. Examples of photochemical induction of strand breaks, light-induced photooxidative damage and the formation of covalent photoadducts between metal complexes and nucleobases are discussed. Consideration is given to approaches being made to improve the affinity and specificity of interaction so as to generate molecular DNA photoprobes for particular DNA sequences or morphologies (e.g. cruciform, Z-DNA, single stranded DNA).