  An elementary introduction into the Seiberg-Witten theory is given. Many
efforts are made to get it as pedagogical as possible, within a reasonable
size. The selection of the relevant material is heavily oriented towards
graduate students. The basic ideas about solitons, monopoles, supersymmetry and
duality are reviewed from first principles, and they are illustrated on the
simplest examples. The exact Seiberg-Witten solution to the low-energy
effective action of the four-dimensional N=2 supersymmetric pure Yang-Mills
theory with the gauge group SU(2) is the main subject of the review. Other
gauge groups are also considered. Some related issues (like adding matter,
confinement, string dualities) are outlined.
