[Refactoring Ruby Edition](http://www.amazon.com/Refactoring-Ruby-Edition-Jay-Fields/dp/0321603508) e [Refactoring: Improving the Design of Existing Code](http://www.amazon.com/Refactoring-Improving-Design-Existing-Code/dp/0201485672/ref=sr_1_1?s=books&ie=UTF8&qid=1376873268&sr=1-1&keywords=refactoring+improving+the+design+of+existing+code) são os livros básicos para utilizar a técnica de maneira fundamentada e ainda, servem de referência para quem trabalha com outras linguagens.