In the present lectures the following topics are considered: general properties of neutrinos, neutrino mass phenomenology (Dirac and Majorana masses), neutrino masses in the simplest extensions of the standard model (including the seesaw mechanism), neutrino oscillations in vacuum, neutrino oscillations in matter (the MSW effect) in 2- and 3-flavour schemes, implications of CP, T and CPT symmetries for neutrino oscillations, double beta decay, solar neutrino oscillations and the solar neutrino problem, and atmospheric neutrinos. We also give a short overview of the results of the accelerator and reactor neutrino experiments and of future projects. Finally, we discuss how the available experimental data on neutrino masses and lepton mixing can be summarized in the phenomenologically allowed forms of the neutrino mass matrix.