Leaving aside invertebrates, which are often microscopic, the smallest land vertebrate is Paedophryne amauensis. This tiny frog was discovered in the jungles of New Guinea, and adults are only 0.27 inch long.
This type of frog is terrestrial, prowling the leaf litter of the forest floor and eating insects even smaller than itself. Due to the fact that this frog was just discovered in 2009 and first published in 2012, not much is known about this creature yet.
At about 1.14 inches, the smallest mammal on Earth is the bumblebee bat. It is the smallest mammal in the world by length, although the 0.06-ounce Etruscan shrew is slightly lighter.