Mesopotamia is the name given to fertile land between the Tigris and Euphrates rivers.
It was the site of the first ever human civilization, and the countries that now site where Mesopotamia once stood are modern day Iraq, Syria, Jordan and Iran.
Cities like Damascus (the capital of modern day Syria) are some of the oldest inhabited cities on Earth. Before the emergence of this region a a settling ground, most humans were nomads who wandered around from location to location in search of food and nourishment.
If you're interested in learning more about this fascinating land, I can suggest a number of sources that are definitely worth looking into:
The British Museum have recently put together a highly commendable 'hub' of web information regarding Mesopotamia: http://www.mesopotamia.co.uk/menu.html