Mountains cover 12% of the earth’s surface and 23% of the Mexican territory. Our goal with this essay is to provide the readers with a current and objective definition of what a mountain is, as well as to inform them in a simple way about the biological importance of mountains as guardians of biodiversity and providers of ecosystem services. To do so, we performed a literature search of the most important works on mountain ecology. Our main result is to recognize mountains as priority conservation sites due to the multiple benefits they provide to humanity. Unfortunately, many of the mountains in the world and in Mexico are under different threats.