Design is an important part of Software Development, and plays a key role in creating extendible maintainable solutions. There are many design principles traditionally associated with Object Oriented programming, yet in recent years languages such as Elixir have tempted many developers away from traditional OO languages. In the talk we will explore the OO design principles known as "SOLID", and apply them to an Elixir case study. We will discuss whether these principles are useful in the functional world, or whether functional languages need a set of design principles of their own. After attending this talk you will have a practical understanding of some design principles that can be applied to Elixir and the use cases they can help solve. Visit website for slides and more details: http://www.elixirconf.eu/elixirconfeu2018/georgina-mcfadyen