Ever wondered if you should try type checking in your Python project, or what it takes to get started with mypy? I will show how to introduce type checking the easy way, one step at a time. Dropbox was an early adopter of type checking and mypy, and we've been gradually adding type annotations to our large production codebases since 2016. Engineers love how type annotations improve the clarity of code, and how mypy can surface hard-to-find bugs. We've learned a lot in the process of annotating millions of lines of code, and in this talk you'll learn battle-tested approaches for adding type checking to an existing codebase. I expect no previous experience with mypy. You'll benefit the most if you've worked on a project with multiple developers.