Abstract
The theory of neutrino oscillations is reviewed. Vacuum mixing of two neutrinos is considered in detail. Experiments aimed at detecting neutrino oscillations at reactors, accelerators and meson facilities are presented, as well as the chlorine solar neutrino experiment, in which fewer neutrinos than predicted by the solar standard model are detected. Also the phenomenon of neutrinos changing flavour as they travel through matter and its application to the solar neutrino problem are described.