The Geometry resulting from the application of the Inversion operation. It can be especially powerful for solving apparently difficult problems such as Steiner's Porism and Apollonius' Problem.
See also Hexlet, Inverse Curve, Inversion, Peaucellier Inversor, Polar, Pole (Geometry), Power (Circle), Radical Line
References
Ogilvy, C. S. ``Inversive Geometry'' and ``Applications of Inversive Geometry.'' Chs. 3--4 in Excursions in Geometry.
New York: Dover, pp. 24-55, 1990.