JSON is the lingua franca of modern APIs and configuration files, and System.Text.Json is the built-in library .NET provides to convert between JSON text and C# objects. This lesson covers what the serializer does, how to control its output, how to read and write JSON without giving up on performance, and the parts of the API used in e-commerce code: serializing a Product, deserializing an order coming back from a checkout API, streaming a large catalog file, and parsing dynamic JSON when the shape isn't known up front.