The name of Normandy originates from the Scandinavian word for 'northman' which reflects the roots of the invaders who came to settle the area in the 9th century AD.
From the 4th century BC, this area of Northern France was inhabited by the Gauls (sometimes referred to as Celts), and became a part of the Roman Empire when Julius Caeser invaded and conquered the Gallic tribes in 50 BC. Prior to this, the Gallic tribes had been in constant conflict with Rome, even going so far as occupying for centuries what is today Northern Italy.
Centuries of the Pax Romana became increasingly disturbed from the 3rd century AD as coastal areas were subjected to Saxon (Germanic coastal tribes from modern day Northern Germany) raids. Other Germanic tribes came overland around the turn of the 5th century and as the Western Roman Empire collapsed the people of this area came to be known as the Franks.
Viking raiders (from Scandinavia) gradually conquered the area from the 9th century and in 911 after a seige of Paris, the Viking leader Rollo was legally granted the land he already possessed in exchange for vassalage to King Charles III of France. This event was massively significant as Rollo's descendant William Duke of Normandy invaded England in 1066 and became king after defeating the Anglo-Saxon Harold Godwinson at the Battle of Hastings.
This resulted in the paradoxical position of William being king of England and the equal of the French king, yet a Duke and vassal of the French king. This situation would lead to centuries of conflict between France and England.
During World War 2, France was occupied in 1940 by Germany. Britain, the United States, Canada and Free France took part in a massive invasion to liberate France in 1940, with the Normandy beaches being the focal point.