The clocks go forward one hour at 1am on Sunday.
The period when the clocks are one hour ahead is called British Summer Time (BST).
There's more daylight in the evenings and less in the mornings.
BST was introduced in 1916 during the First World War in a bid to save money.
The current system has been in place since 1972.
The lighter evenings are said to reduce road collisions and crime.
It is also argued that BST is good for physical and psychological health, particularly in terms of relieving the symptoms of seasonal affective disorder.