Command Query Responsibility Segregation (CQRS) is a software architectural pattern that separates the operations that modify data (commands) from those that retrieve data (queries). This separation allows for more efficient handling of each operation, as commands can focus on changing the state of the system, while queries can optimize data retrieval without being affected by the complexities of data modification. By using CQRS, developers can scale applications more effectively and improve performance. It also enables the use of different data storage solutions for commands and queries, allowing for tailored optimizations. This pattern is often used in conjunction with Event Sourcing to maintain a clear history of changes.