The underlying concept of design patterns has been around in the software engineering industry since the very beginning, but they weren’t really so formalised. Design Patterns: Elements Of Reusable Object-Oriented Software written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides — the famous Gang of Four (GoF)—was instrumental in pushing the formalised concept of design patterns in software engineering. Now, design patterns are an essential part of software development and have been so for a long time.