Understand how software is changed without creating problems: add features, fix bugs, improve design, and optimize performance. Write tests that protect your software from new problems. Work with legacy code that is not object-oriented. Outdated code becomes good code with this book! Legacy code refers to software without tests and a chaotic codebase that somehow works, but nobody knows why. Almost every company deals with outdated code that doesn't run well or has performance issues. Michael Feathers shows software developers in this book how to achieve more performance and reliability from old code and how to make it more manageable. The reader learns how to modify software and add features without degrading it, as well as how to write tests that are pre-restored.