# Entity: Objects with Identity > [!Note] > An **Entity** is a mutable domain object defined by its **unique identity**, responsible for tracking concepts over its **lifespan**, and warranting individual accountability within the model. **Entities** embody domain concepts that require distinct, enduring identities—each instance carries a **key or identifier** that distinguishes it from all others. Unlike immutable value objects, an **Entity's** state is **mutable**, evolving over time as the business context changes. Because **Entities** represent important business artifacts, they carry **responsibility** for behaviors and data that must be followed and audited individually. Their **lifecycle** spans multiple operations and transactions, reflecting the ongoing journey of the domain concept they model. --- ## References - Vernon, V. (2016). _Domain-driven design distilled_. Addison-Wesley Professional. - Vernon, V. (2013). _Implementing domain-driven design_. Addison-Wesley Professional. - Khononov, V. (2021). _Learning domain-driven design: Aligning software architecture and business strategy_. O’Reilly Media. - Alammar, J., & Grootendorst, M. (2024). _Hands-on large language models: Language understanding and generation_. O’Reilly Media. - Evans, E. (2003). _Domain-driven design: Tackling complexity in the heart of software_. Addison-Wesley Professional. - Millett, S., & Tune, N. (2015). _Patterns, principles, and practices of domain-driven design._ Wrox.