Design Patterns: Elements of Reusable Object-Oriented Software - by Erich Gamma, Richard Helm, Ralph Johnson & John Vlissides

"Design Patterns: Elements of Reusable Object-Oriented Software" by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, often referred to as the "Gang of Four," is a groundbreaking work in software engineering. It introduces 23 fundamental design patterns that provide time-tested solutions to common object-oriented design problems. The book categorizes patterns into creational, structural, and behavioral types, offering a vocabulary for developers to create more modular, flexible, and maintainable code.