Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In theoretical physics, Montonen Olive duality is the oldest known example of S-duality or a strong-weak duality. It generalizes the electro-magnetic symmetry of Maxwell''s equations. It is named after Finnish Claus Montonen and British David Olive. In a four-dimensional Yang-Mills theory with N=4 supersymmetry, which is the case where the Montonen Olive duality applies, one obtains a physically equivalent theory if one replaces the gauge coupling constant g by 1/g. This also involves an interchange of the electrically charged particles and magnetic monopoles. See also Seiberg duality.In fact, there exists a larger SL(2,Z) symmetry where both g as well as theta-angle are transformed non-trivially.