Working with a mature codebase is a bit like dealing with a teenager - things are mostly functional, occasionally unpredictable, and constantly reminding you of your past decisions. In this talk, I’ll share a collection of hard-earned lessons and useful patterns from maintaining and evolving a 15-year-old Django project. From keeping your legacy front end framework in sync with your shiny new tool, to taming complex APIs and tracking performance with precision, this is a tour through a handful of useful patterns picked up working with a stable codebase through the years.