Behavior-Driven Development (BDD) is an agile software development methodology that extends Test-Driven Development (TDD) by writing test cases in natural language that non-programmers can read. BDD emerged in 2003 when Dan North sought to bridge the gap between business stakeholders and technical teams, creating a shared understanding of requirements through concrete examples. The methodology uses Gherkin syntax—a domain-specific language with keywords like Given-When-Then—to describe system behavior in plain English, transforming these human-readable scenarios into executable specifications that serve as both tests and living documentation. A key insight: BDD is fundamentally a collaboration practice focused on discovering unknowns through conversation (the "Three Amigos" approach), not merely a testing technique, making early discovery workshops more valuable than the automation that follows.