Birefringence in diamond is an anomalous optical property. Its occurrence is the result of strain in the diamond lattice, modifying its natural isotropic properties. However, an understanding of the resultant patterns can give us insights into the causes of the strain, which in turn can provide us with an idea of the growth and/or stress history of the diamond. The simplicity of imaging a diamond between crossed polarizers means that observing its possible birefringence pattern is a useful tool for learning about its history. In this paper, the causes of birefringence in diamond are reviewed and considered in the context of a modern understanding of diamond as well as the modern analytical techniques available to study them.