The Medium Ground-finch (Geospiza fortis) is a species of bird in the Emberizidae family.

It is endemic to Ecuador. Its natural habitats are subtropical or tropical dry forests and subtropical or tropical dry shrubland.

One of Darwin's finches, the species was the first which scientists have observed evolving in real-time due to competition from another species. Specifically, the beak of the medium ground-finch reduced in size over two decades in order to eat smaller seeds, as larger species which were introduced to their habitat were eating the larger ones, leaving the finch with an inadequate food supply.