Information theory usually abstracts from the underlying physical carriers of information: There is no "hard-drive information" any different from "newspaper information". This is because one type of information can be transformed into another one in a lossless fashion, and hence the actual physical carrier does not matter when it comes to thinking about what ways of processing of information are possible. Things change dramatically, however, if single quantum systems - such as trapped ions, cold atoms, or light quanta - are taken as elementary carriers of information. This course will give an introduction into what is possible pursuing this idea. We will discuss applications of quantum key distribution (allowing for the secure transmission of information), quantum computing (giving rise to computers that can solve some problems faster than conventional supercomputers), quantum simulation (allowing to simulate other complex quantum systems) and sensing devices. For this, we will develop the underlying quantum information theory, with notions of entanglement taking center stage. These applications are subsumed into what is now often called quantum technologies. Specific emphasis will finally be put onto elaborating on the intersection of quantum information theory on the one hand and condensed-matter physics on the other, where new perspectives arise.