Optical Coherence Tomography (OCT) is an imaging technique originally developed for high-resolution 3D imaging of the human eye. In 2004, Targowski et al. and Liang et al. first reported its application to paintings, demonstrating that it was possible to produce cross-section images noninvasively with this technique. In 2005 Liang et al. explored further applications such as imaging of underdrawing at a resolution and contrast greater than that achievable with infrared reflectography. Since then the authors have been conducting a project to investigate systematically the potential of OCT as a new tool in the non-invasive examination of paintings and to design an OCT optimised for use in museums. This article discusses recent developments in this work and presents examples of the use of OCT on paintings undergoing conservation treatment in the National Gallery, London.