Occitan is directly descended from Latin, and is therefore cousin to other Romance languages such as Catalan, Castillian (now generally called Spanish), Portuguese, Italian, French, Romanian and Romanche.
In the Middle ages Occitan was often called Romana, a reminder of its Roman origins. Similar reminders are only slightly less obvious in Romanian, Ramanche and Romance, the name of the whole language sub-family.
This evolution of popular Latin was influenced by local languages spoken before the arrival of the Romans, which accounts for much of the difference between members of the Romance family of languages.