Imaging the secondary stars in cataclysmic variables

The secondary, Roche-lobe filling stars in cataclysmic variables (CVs) are key to our understanding of the origin, evolution and behaviour of this class of interacting binary. We review the basic properties of the secondary stars in CVs and the observational and analysis methods required to detect them. We then describe the various astro-tomographic techniques which can be used to map the surface intensity distribution of the secondary star, culminating in a detailed explanation of Roche tomography. We conclude with a summary of the most important results obtained to date and future prospects.