# In depth

- [Secure By Design](/in-depth/secure-by-design.md)
- [Architecture](/in-depth/architecture.md)
- [How do VPN statistics work](/in-depth/architecture/how-do-vpn-statistics-work.md)
- [Security concepts](/in-depth/architecture/security-concepts.md)
- [MFA Architecture](/in-depth/architecture/architecture.md)
- [Architecture Decision Records](/in-depth/architecture-decision-records.md): What are Defguard's Architecture Decision Records?
- [1.6](/in-depth/architecture-decision-records/1.6.md)
- [1.5](/in-depth/architecture-decision-records/1.5.md)
- [1.4](/in-depth/architecture-decision-records/1.4.md)
- [1.3](/in-depth/architecture-decision-records/1.3.md)
- [Pre-1.3](/in-depth/architecture-decision-records/pre-1.3.md)
- [Roadmap](/in-depth/roadmap.md): This is a high-level project roadmap of planned features.
- [Release cycle](/in-depth/release-cycle.md)
- [Client application feature compatibility](/in-depth/client-application-feature-compatibility.md)