# In depth

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