**4. Summary**

We attempt to review germanium elemental materials and summarize the highlights of the history of germanium. Although the complete story of germanium would be lengthy, we have tried to highlight the material and device aspects of germanium. From the Ge application perspective, there are a number of examples; but the main applications could be categorized into five areas such as IR optics; fiber optics; polyethylene terephthalate—PET; electronic and solar; and phosphors, metallurgy, and organic applications. After the first invention of a transistor in 1947, which is arguably perceived as the most important invention in the twentieth century, and silicon replacement, germanium in electronics remarkably returns. The steady-fast increase of germanium application in IR and fiber optics is interesting as well. Furthermore, it is expected that more studies of germanium nanocrystals could contribute to the increased attention to research and development of new germanium applications in near future.
