Behavior driven development (BDD), also spelled behaviour driven development, is an Agile practice where developers, testers and business stakeholders agree on how software should behave before it is built. The team describes that behavior as concrete examples written in plain language, usually in a Given-When-Then format, and then turns those examples into automated tests.

This glossary page covers how BDD grew out of TDD, how the three amigos meeting works, and what a Gherkin scenario looks like in practice. It also lists the common tools like Cucumber, SpecFlow and Behave, and explains where BDD helps and where it slows a team down.