A course of lectures on mesoscopic quantum interference phenomena: we begin with a qualitative survey of the manifestations of quantum phase coherence and interaction in mesoscopic structures. This will be followed by a more methodologically oriented part which aims to introduce the construction of effective field theories of mesoscopic systems. The remaining sections of the course will be devoted to the discussion of various applications, with an emphasis on recent developments. Specifically, we will discuss electron-electron interaction phenomena, review the status of the ballistic ([sigma]-model and its application to problems of 'quantum chaos', and introduce basic elements of mesoscopic superconductivity. Some emphasis will be given to the discussion of the concept of seven 'new' symmetry classes. We discuss why the three-fold symmetry classification of Wigner and Dyson is not exhaustive and where 'non-standard' symmetries are realized. This will be followed by the discussion of a number of applications, notably disordered hybrid superconducting-normal structures, dirty d-wave superconductvity, and chiral fermion systems.