The Onion Architecture term was coined by Jeffrey Palermo in 2008. This architecture provides a better way to build applications for better testability, maintainability, and dependability on the infrastructures like databases and services.

• Maintainability
• Testability
• Loosely coupled
• Concrete implantation
• Domain entities are core and center part. It can have access to both the database and UI layers
• The internal layers never depend on the external layer

• Domain Entities Layer
• Repository Layer
• Service Layer
• UI (Web/Unit Test) Layer