Intersubband nanostructures are the key enabling technology for long-wavelength optoelectronics. Because mid-infrared and terahertz wavelengths are below the bandgap of most semiconductor materials, one cannot rely on interband transitions when manipulating them. Instead, one must rely on intersubband transitions, devices that exploit the quantum nature of electrons to make artificial atoms. Perhaps the most famous intersubband device is the quantum cascade laser (QCL), a semiconductor source of light at these wavelengths that is chip-scale. A key theme of our work is the design and characterization of new intersubband systems, particularly terahertz QCLs.