This book focuses on the linkages between very high energy (TeV or 10¹² electron-volt) gamma-ray astronomy and the interstellar medium (ISM), and the key science questions expected to be answered. Their joint study is essential if we are to understand the nature of gamma-ray emission and hence shed light on where extreme cosmic-rays and electrons are being accelerated in our galaxy. Since TeV neutrinos are also intimately tied to the production of gamma-rays of similar energy, we would also extend our discussion to this field.