One of the biggest films of the summer is out today - Dunkirk.
Harry Styles will be making his acting debut in the movie, which tells the story of a very important event which took place in World War II.
Harry has said: "It's a very emotional story."
Christopher Nolan, who directed the new film, told BBC News: "What drew me to this story is it is a survival story first and foremost."
But what is this story and why was this event in history so important?
The Dunkirk story took place during World War II.
World War II was a huge war between 1939 and 1945 involving many countries around the world, who were fighting each other for power.
There were many important battles and military missions during the war.
Dunkirk was one of these important military missions, which happened in May 1940.
During the war, some countries joined together to fight with each other.
British, French and Belgian soldiers were on the same side. They were known as the Allied troops.
They were fighting against the Germans.
In 1940, the Germans invaded France. They also invaded Belgium and Holland.
They beat the British, French and Belgian soldiers back to the port of Dunkirk, which is on the north coast of France.
The Allied troops found themselves trapped at the beaches there, surrounded by the Germans.
So the British prime minister at the time, Winston Churchill, ordered a fleet of 900 boats to travel from Britain to Dunkirk to rescue the soldiers and bring them back to England to safety.
More than a quarter of a million people were rescued from the beaches of Dunkirk during the mission.
World War II carried on for another five years after the mission on the Dunkirk beaches took place.
The story of the Dunkirk rescue is still told today as many people risked their lives to save so many others.
Mark Rylance, who is an actor in the film, says: "It was a miraculous retreat."
It was important because even though the British Army and Allies had to flee France, it meant that they lived to fight another day and they eventually went on to win the war.
Dunkirk is a 12A film released on Friday 21 July in the UK