An elementary introduction into the Seiberg-Witten theory is given. Ev
ery effort is made to get it as pedagogical as possible, and within a
reasonable size. The selection of the relevant material is heavily ori
ented towards graduate students. The basic ideas about solitons, monop
oles, supersymmetry and duality are reviewed from the first principles
, and they are illustrated on the simplest examples. The exact Seiberg
-Witten solution to the low-energy effective action of the four-dimens
ional N = 2 supersymmetric pure Yang-Mills theory with the gauge group
SU(2) is the main subject of the review. A generalization of that app
roach to other gauge groups is also discussed in some detail. Some rel
ated issues (adding matter, confinement, string dualities) are outline
d.