ADO.NET is a set of classes in the .NET Framework that enables developers to interact with databases. It provides a way to connect to various data sources, execute commands, and retrieve results. ADO.NET supports both connected and disconnected data access, allowing applications to work with data efficiently. The architecture of ADO.NET consists of two main components: DataSet and DataReader. The DataSet is an in-memory representation of data that can hold multiple tables and relationships, while the DataReader provides a fast, forward-only way to read data from a database. Together, they facilitate seamless data manipulation in .NET applications.