# In depth

- [Secure by design](https://docs.defguard.net/in-depth/secure-by-design.md)
- [Architecture](https://docs.defguard.net/in-depth/architecture.md)
- [How do VPN statistics work](https://docs.defguard.net/in-depth/architecture/how-do-vpn-statistics-work.md)
- [Security concepts](https://docs.defguard.net/in-depth/architecture/security-concepts.md)
- [MFA Architecture](https://docs.defguard.net/in-depth/architecture/architecture.md)
- [Architecture Decision Records](https://docs.defguard.net/in-depth/architecture-decision-records.md): What are Defguard's Architecture Decision Records?
- [2.0](https://docs.defguard.net/in-depth/architecture-decision-records/2.0.md)
- [1.6](https://docs.defguard.net/in-depth/architecture-decision-records/1.6.md)
- [1.5](https://docs.defguard.net/in-depth/architecture-decision-records/1.5.md)
- [1.4](https://docs.defguard.net/in-depth/architecture-decision-records/1.4.md)
- [1.3](https://docs.defguard.net/in-depth/architecture-decision-records/1.3.md)
- [Pre-1.3](https://docs.defguard.net/in-depth/architecture-decision-records/pre-1.3.md)
- [Client application feature compatibility](https://docs.defguard.net/in-depth/client-application-feature-compatibility.md)
- [Defguard Open Organisation](https://docs.defguard.net/in-depth/defguard-open-organisation.md)
- [Product Development Procedure](https://docs.defguard.net/in-depth/defguard-open-organisation/product-development-procedure.md)
- [Roadmap](https://docs.defguard.net/in-depth/defguard-open-organisation/roadmap.md): This is a high-level project roadmap of planned features.
- [BoringTun](https://docs.defguard.net/in-depth/boringtun.md)


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