We have all come across examples of materials failure, whether it be the broken rail which caused trains to be delayed or the cup that broke when dropped on the ﬂ oor. A material can be considered to have failed when its ability to completely satisfy the original design function ceases. Failure can occur as a result of a number of causes, e.g. the material may fracture or perhaps degrade as a result of corrosion. In this chapter, we consider the causes of such failures and the methods that can be adopted to prevent, or at least, delay failure.