API versioning is a systematic approach to managing changes in web APIs while maintaining backward compatibility for existing clients. It enables API providers to introduce new features, fix bugs, and evolve their services without breaking client integrations. Proper versioning strategies balance the need for innovation with the stability requirements of production systems. A well-designed versioning approach considers not just how versions are communicated (URI, headers, or media types), but also the complete lifecycle: deprecation timelines, migration support, monitoring adoption, and communicating changes effectively to consumers.