All four of Wales' police forces are cracking down on drivers and passengers who don't wear their seatbelts.
The 'Belt Up!' campaign aims to raise awareness of the dangers of not using a seatbelt, and will also see more officers stopping vehicles and issuing fines.
It will run until 24 March.
Brothers Kyle and James Smith from Wenvoe in the Vale of Glamorgan were travelling in the same car, which crashed in 2005.
Kyle was 16, not wearing a seatbelt, thrown from the vehicle and died.
James was 15, wearing a seatbelt and survived.
The law requiring all drivers to wear seatbelts was introduced 30 years ago.