A Design Pattern is an existing design solution to a common problem that captures experience and good practice in a form that can be reused. All patterns are guided by a small number of software design principles (see Chapter 2 Table 1). A design pattern is normally not a complete solution that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations, an abstract representation that can be implemented in different ways. Such a description simplifies communication between software practitioners. However you will find efforts available on the Internet to provide code templates in specific languages for some patterns. Patterns are not essential in the development of software solutions but are valuable sources of advice and guidance. Patterns were introduced by Christopher Alexander in the field of building architecture, where he documented reusable architectural proposals for producing good quality building designs. In 1995 Gamma et al. [1] (the “Gang of Four” – GoF) adapted the concept of patterns for software development and catalogued 23 detailed design patterns aimed at meeting some commonly-recurring object-oriented design needs, albeit at the level objects (component/ subsystem interactions). Simplified explanations of these 23 design patterns are presented in [2]. Since then many software design patterns, pattern types and pattern catalogues have emerged, having emanated from different software development communities building different types of system using different methods, languages and tools, which also explains different naming conventions.