The most important aim of this chapter is to describe what an evolutionary algorithm is. This description is deliberately based on a unifying view presenting a general scheme that forms the common basis of all evolutionary algorithm (EA) variants. The main components of EAs are discussed, explaining their role and related issues of terminology. This is immediately followed by two example applications (unlike other chapters, where example applications are typically given at the end) to make things more concrete. Further on we discuss general issues of the working of EAs. Finally, we put EAs into a broader context and explain their relation with other global optimisation techniques.