The Universal Serial Bus Implementers Forum (USB-IF) has taken the position that all USB products must function together without problems. Each class of USB product must pass specific testing, and the devices must also pass testing for interoperability. This also means that low-speed, full-speed, and high-speed devices must function together in the same USB tree. Full-speed devices must be able to work properly in a high-speed environment, and vice versa. In the beginning, compliance testing for USB devices was a rather cursory process of plugging in simply to see if the device enumerated. Since then, compliance testing has evolved into a robust compliance program with detailed test matrices and multiple tests, including tests for interoperability. Products that pass today’s compliance testing are allowed to display the new, high-speed logo for USB 2.0 a logo which gives users the confidence that all USB devices will work together, whether low-speed, full-speed, or high-speed.