The need for environmental sensing, trace gas detection, control of hazardous materials, and pollution control is of crucial importance to our modern industrial society. This is because our quality of life, safety and environmental legacy are all affected by the environment we live in and leave behind. Most of the important chemical compounds such as green house gases, drugs, explosives and hazardous chemicals can be sensed and detected by their fingerprint absorption lines that fall into the infrared spectral region from 2-20 µm. To solve this real world, macro-scale problem, the IR-ON special research program aims to utilize nanostructures to overcome the shortage of photonic devices for this wavelength region and to make significant advances in their fundamental understanding for development of future devices. Realization of semiconductor nanostructures offers fascinating perspectives both for fundamental science and for development of new electronic and photonic devices. Since semiconductor quantum dots resemble “artificial” atoms, their apparent quantum nature can be combined with advantages of the “classical” semiconductor devices. In this way, these local ensembles of semiconductor atoms can be contacted with leads, integrated in circuits and built with high integration levels. Confinement of charged carriers to the nanometer scale leads to quantized energy levels with energy spacings corresponding to the infrared spectral region. Thus, nanostructuring of semiconductors adds new functionality – infrared optical activity. The goal of the joint IR-ON research program is to control, investigate, understand and make practical use of this infrared optical activity. Drawing on the broad expertise and infrastructure available at the participating institutions, this SFB is focused on five main interdisciplinary research areas: (1) Nanofabrication of novel infrared materials by combination of self-organization processes with nanolithography. This allows the realization of engineered nanostructures as basis for the overall SFB goals. (2) New types of analysis methods with high spatial resolution will be developed and employed to obtained detailed structural, optical and electronic information on individual nanostructures. This will yield not only a better understanding but also important feedback and input for the fabrication processes as well as for theoretical modeling and design of novel devices. (3) Infrared and THz spectroscopy will reveal the electronic structure as well as time-dependent dynamics of optical processes in infrared nanostructures, which are crucial for the design of devices and prediction of their performance. (4) Theoretical methods will be developed and implemented for ab initio description of nanostructure growth and structure, as well as for prediction of electronic levels and optical effects up to the level of device simulations. (5) Finally, novel infrared nanostructure devices will be realized, continuous-wave infrared lasers, single photon sources and detectors as well as novel photonic band gap structures.