MongoDB is a database with a flexible schema, but the experts at MongoDB recommend that you store documents with the same or similar schema in a single collection. So what's the point of a flexible schema anyway? Migrations. Data migration is MongoDB's killer feature. In this talk, I will describe the types of schema change that are required as an application matures. I'll cover the different approaches to migration available to MongoDB developers, along with their benefits and tradeoffs, and finally, I'll cover the code techniques and database features you can use to manage the complexity of working with different schemas simultaneously.