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Refactoring by Martin Fowler is a great one https://www.amazon.com/Refactoring-Improving-Existing-Addison-Wesley-Signature/dp/0134757599/ https://www.amazon.com/Refactoring-Improving-Existing-Addiso... Design Patterns is also very well known https://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612 https://www.amazon.com/Design-Patterns-Elements-Reusable-Obj...