The Zurich Instruments HF2LI (high-frequency, 2 inputs) is a digital lock-in amplifier covering the frequency range between DC and 50 MHz. It features 2 physical input channels so that it can replace 2 devices in many measurement setups. The 128-bit digital signal processing delivers superior precision thus boosting both the noise performance and the dynamic reserve. With these unprecedented capabilities, the HF2LI brings lock-in amplification to a new level and enables new applications in a frequency range that was previously tied to analog instrumentation. The computer is connected by a high-speed USB interface, which allows data acquisition at high rates. The HF2LI is delivered with a fully featured graphical user interface and a choice of programming interfaces that greatly add to the usability of the instrument.