The graphical construction for the representation of the state of stress at a point within a continuum region is generally attributed to the German engineer Otto Christian Mohr. Although the use of graphical techniques in structural and solid mechanics has been an important area of activity both for engineering calculations and stress analysis, particularly in the eighteenth and nineteenth centuries (see, e.g., Todhunter and Pearson (1886, 1893) and Timoshenko (1953), the contributions of Karl Culmann and Otto Mohr to the development of this area are regarded as being particularly significant. Despite the passage of time these graphical constructions have continued to serve as efficient educational tools for the visualisation of difficult concepts related to the representation of three-dimensional states of stress, particularly in relation to the description of failure states in materials. The fact that the techniques developed in relation to the stress state at a point that can be represented in terms of a stress matrix of rank two or a second-order tensor implies that the procedures are equally applicable to the description of other properties and states in continua, which can be described in a similar manner. Examples include the description of moments of inertia of solids, flexural characteristics of plates and the hydraulic conductivity characteristics of porous media, etc. The purpose of this Appendix is to present a brief outline of the significant features of Mohr circles and to develop the basic equations applicable to the three-dimensional graphical representation of the stress state at a point.