Powerful coherent light with a spectrum spanning the mid-infrared (MIR) spectral range is crucial for a number of applications in natural as well as life sciences, but so far has only been available from large-scale synchrotron sources1. Here we present a compact apparatus that generates pulses with a sub-two-cycle duration and with an average power of 0.1 W and a spectral coverage of 6.8–16.4 μm (at −30 dB). The demonstrated source combines, for the first time in this spectral region, a high power, a high repetition rate and phase coherence. The MIR pulses emerge via difference-frequency generation (DFG) driven by the nonlinearly compressed pulses of a Kerr-lens mode-locked ytterbium-doped yttrium–aluminium–garnet (Yb:YAG) thin-disc oscillator. The resultant 100 MHz MIR pulse train is hundreds to thousands of times more powerful than state-of-the-art frequency combs that emit in this range2–4, and offers a high dynamic range for spectroscopy in the molecular fingerprint region4–7 and an ideal prerequisite for hyperspectral imaging8 as well as for the time-domain coherent control of vibrational dynamics9–11.