Software mining is related to both data mining and reverse engineering. It is focused on mining software artefacts such as code bases, program states and structural entities for useful information related to the characteristics of a system. This paper provides an introduction to the field. It first reviews a representative selection of the ways software mining has been applied. It then divides software mining into three subcategories and explains each one in detail. Finally this paper summarises some of the advantages and limitations of software mining, both now and in the future. These advantages and limitations have been informed by the author's own research applying software mining to the field of User Interface generation.