When a drug binds to DNA, its electronic structure is perturbed, and it perturbs the DNA's electronic structure. The resulting change to the electronic spectroscopy can be used to probe the drug-DNA interaction. This chapter outlines how circular and linear dichroism spectroscopy can be used to provide information about drug-DNA systems. Circular dichroism spectroscopy involves measuring the difference in absorption of left and right circularly polarized light. It is uniquely sensitive to the helicity of the molecules being studied. Linear dichroism, as the name implies, involves measuring the difference in absorption of light linearly polarized parallel and perpendicular to an orientation axis. Linear dichroism provides information about the relative orientations of subunits of an interacting system. The material presented in this chapter is by no means comprehensive; the aim is to enable the user to collect reasonable quality data and to interpret it.