Introduction to magnetic monopoles

One of the most basic properties of magnetism is that a magnet always has two poles, north and south, which cannot be separated into isolated poles, i.e. magnetic monopoles. There are strong theoretical arguments why magnetic monopoles should exist, but in spite of extensive searches they have never been found. This article gives an introduction to theoretical and experimental aspects of magnetic monopoles and discusses their role in our understanding of fundamental physics, both historically and today.