Ask HN: How do you ensure your documentation stays up to date?

Keeping your documentation updated and relevant when working in a large codebase seems to be a difficult task. When a lot of developers are making different changes some might forget to update different pieces of documentation in different places. I've seen some companies that don't have any documentation but try to make their code self-documenting in order to avoid this problem altogether.

How does your organization make sure that your documentation stays relevant? Are there any tools or techniques you use to help with this?