  On any convex domain in $\mathbb{R}^n$ we can define the Hilbert metric. A
projective transformation is an example of an isometry of the Hilbert metric.
In this thesis we will prove that the group of projective transformations on a
convex domain has at most index 2 in the group of isometries of the convex
domain with its Hilbert metric. Furthermore we will give criteria for which the
set of projective transformations between two convex domains is equal to the
set of isometries of the Hilbert metric of these convex domains. Lastly we will
show that $2$-dimensional convex domains with their corresponding Hilbert
metrics are isometric if and only if they are projectively equivalent.

Metric Geometry