Radiation therapy of lung cancer is among the most common and important areas of image-guided radiation therapy. Imaging simulations including computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography with 2-fluorine-18 fluoro-2-deoxy-D-glucose (FDG-PET) and FDG-PET combined with CT (FDG-PET/CT) are currently being used for clinical assessment of lung cancer. Recent technological advances in these imaging systems hold great promises to produce marked improvements toward more precise treatment of lung cancer. In this chapter, we will focus on recent advances in CT, MRI, PET, and other imaging methods in lung cancer applications, and discuss their potentials and limitations for use in clinical practice.