Unidentified TeV Sources and the Interstellar Medium

TeV gamma-ray astronomy and the interstellar medium (ISM) are intimately linked via fundamental particle physics processes. Over 100 TeV gamma-ray sources in our galaxy are now known, although a large fraction of them remain unidentified either in terms of their countpart accelerator and/ or the type of particles responsible for the emission. With the forthcoming Cherenkov Telescope Array (CTA) offering arc-minute angular gamma-ray resolution, similar resolution ISM surveys will be needed to help understand the variety of particle astrophysics issues the CTA will uncover in its Galactic plane and other survey science. In this review I will look at the status of the unidentified TeV gamma-ray sources, the key particle physics issues, the forthcoming ISM surveys, and then see how these will link in to CTA.