Mitochondria are not only the ‘energy powerhouse of the cells’, but they also represent essential semi-autonomous cellular components. Over the last decades, research focusing on mitochondria has exponentially increased, principally because these organelles are involved in fundamental cellular processes. The maintenance of ion homeostasis is at the basis of the mitochondrial physiology and several types of channels play a critical role in this process. This work gives a simple but detailed description of the mitochondrial physiology, with particular attention to ion homeostasis and offers an up-to-date description of the modulation of mitochondrial potassium homeostasis by pharmacological tools, also in pathological conditions such as cancer.