Zorro is a Hackystat application that is designed to help you learn to use the "Test-Driven Development" (TDD) style for Java software development and, in conjunction with other Hackystat measurements and analyses, help you to understand the impact of TDD on your software and your way of developing it. This chapter begins with an overview of the Test Driven Development style of development. It then shows how you can use Zorro to gain insight into how you use (or don't use) TDD during software development. It concludes with a selection of resources you can use to learn more about TDD.