Magnetic reconnection is a fundamental plasma–physics process that is of great importance for the Sun, the Earth9s magnetosphere and all astrophysical objects which have magnetic fields. It is a process central to the generation of magnetic fields in stars and also plays a major role in the heating of solar and stellar coronae. The development of both large (e.g. flares) and small (e.g. coronal bright points) dynamic phenomena observed on the Sun depends on reconnection and it is likely that reconnection may also be important for the acceleration of solar and stellar winds. It is 50 years since the first seeds of ideas for magnetic reconnection were sown and over 40 years since the classic Sweet–Parker mechanism was suggested. Since then the majority of the research has focused on reconnection in two dimensions. However, in the last few years attentions have turned to understanding the intricacies of reconnection in three dimensions. In this paper, the classical aspects of two–dimensional reconnection are reviewed, together with various mechanisms for reconnection in three dimensions, in particular, spine, fan and quasi–separatrix layer reconnection. The paper is then rounded off with examples of some solar phenomena where reconnection is believed to be present. In particular, the heating of some observed small–scale events in the corona is investigated and the question of quiet coronal heating due to nanoflares and microflares is addressed.