The notion of the active role of mitochondria in the decoding and shaping of intracellular Ca2+ signals dates back at the end of the 19th century. However, the identity of the molecule(s) involved in Ca2+ ion transport into mitochondria remained elusive for decades. Only in the last ten years, the factors, and the relative coding genes, mediating Ca2+ entry in mitochondria started to be genetically and biochemically described. The gene for the pore-forming unit of the mitochondrial Ca2+ channel was discovered in 2011, and its product was named mitochondrial Ca2+ uniporter or MCU. The mitochondria Ca2+ uptake regulator 1 gene, MICU1, was cloned one year before, in 2010. The increasing interest of the scientific community towards mitochondrial Ca2+ signaling and metabolism in the subsequent years led to the identification of many other MCU components and to the description of their 3D structure and physiological role. Here, we will present a brief overview of the land marking discoveries in the history of mitochondrial Ca2+ studies.