Number 10 is among the buildings that will turn their lights out in an hour's time to mark the moment Britain declared war on Germany and joined the First World War.
Are you joining in the Lights Out event? Post pictures of your "moment of reflection" on our Facebook page.
As the Lights Out event to remember those who fought and died in WWI happened last night ITV asked our viewers what they did to take part.
Lights on some of Britain's most famous landmarks were extinguished between 10pm and 11pm to remember those who died in WWI.