External cavity quantum-cascade lasers (QCLs) emitting in the long-wave infrared (LWIR) around 10 μm and in the mid-wave infrared (MWIR) around 5.2 μm have been realized. The coupling facet of the QC chips was anti-reflection coated and the optical feedback was provided by a diffraction grating arranged in a Littrow configuration. The active regions of the gain elements were based on bound-to-continuum designs having broad gain curves (Approx = to 300 cm-1 full width at half maximum). The LWIR laser was operated in pulsed mode on a thermoelectric (TE) cooler. It could be tuned over a frequency range of 150 cm-1 from 9.1 to 10.55 μm with a peak power ⩾ 30 mW. The MWIR laser was operated in continuous-wave (CW) mode on a TE cooler. It could be tuned over more than 170 cm-1 from 4.95 to 5.4 μm and was single-mode over more than 140 cm-1. Its output power was in excess of 5 mW over 130 cm-1. This broad tunability (10 times more than that of distributed-feedback QCLs) enables new applications of QCLs in high-resolution infrared spectroscopy.