Plasmas are ionised gases in which atoms have dissociated into positively charged ions and negatively charged electrons and, to an extent, can move independently from one another. More than 99% of the visible Universe is estimated to be in the plasma state, thus making it the most important of the four fundamental states of matter. This chapter introduces the ways of mathematically treating plasma and lays the foundation for the work in this thesis. Most of the background information here can be found in introductory textbooks (e.g. Boyd and Sanderson 2003).