Colloidal quantum dots (CQDs) have been studied extensively because of their wide color tunability, solution-processing potential and many potential applications such as fluorescence sensing, photovoltaics, detectors, and generally printable electronics. Most of the research is based on the interband absorption or fluorescence between conduction band and valence band states. However, there is also the possibility of using the intraband transitions, the transitions between states within the conduction or valence bands. To take advantage of the intraband transitions, it is essential to have some carrier doping in the lowest quantum states. However, no stable carrier doping in ambient condition had been observed in CQDs before the air-stable n-doped HgS1 and HgSe QDs. This makes it now possible to investigate the intraband photoresponse. In this talk, I will introduce the synthesis of n-doped HgS and HgSe QDs, and their fascinating optoelectronic properties, focusing on their intraband optical properties of absorption and luminescence and especially the first intraband photoconductivity observed with colloidal quantum dot solids. The intraband photoresponse covers the mid-infrared atmospheric transparency, 3 to 5 microns. Colloidal Quantum Dots Intraband Photodetection is a striking new possibility with solution-processed materials, fully taking advantage of the quantum confinement, as well as a novel direction for research on infrared devices.