In this report, we summarize our recent achievements in free-space communications in the mid-infrared (MIR) region enabled by directly modulated quantum cascaded laser (QCL) at 4.65 mu m (similar to 65 THz). We have experimentally demonstrated a multigigabit free- space transmission link in the lab environment with the QCL operating at room temperature. The QCL chip is mounted on a commercial QCL mount with a water-cooled Peltier element. Multilevel modulation formats at different baud rates are generated and combined with the laser driving current at a custom-made bias-tee to drive and modulate the QCL. A commercial mercury cadmium telluride (MCT, HgCdTe) photovoltaic (PV) MIR detector with a built-in trans-impedance amplifier was used to receive the MIR free-space signal. With the receiver to be the bottleneck of the system bandwidth, the end-to-end 3-dB bandwidth was measured to be around 320 MHz, and the 6-dB bandwidth was around 450 MHz. We have successfully demonstrated up to 6 Gbps free space transmission with multilevel modulation formats, assisted with effective digital equalization techniques despite the limited bandwidth.