This article presents a short review of the knowledge concerning carbon nano-onions, also known as onion-like carbon or multi-layered fullerenes. Currently, these nanostructures are some of the most fascinating carbon forms. We can only find approximately 2000 articles under the entry of “carbon onion” in the Web of Science. Surprisingly, there have been ∼40,000 citations since their discovery, and the interest in these nanostructures is still growing. In the last three years, 5000 citations per year have been reported. This means that researchers have noted the unusual nature of these carbon nanostructures. In this article, we review the most important literature reports in this area, which in a condensed way, present these nanostructures, their production methods, their unusual physical and chemical properties and their potential uses.