To mark Holocaust Memorial Day yesterday (27 January), a series of landmarks including the BT Tower, London Eye, Battersea Power Centre and Blackpool Tower were lit up in purple.
The theme of HMD 2021 is "Be the light in the darkness".
Households took part in the moment yesterday evening, called "Light the Darkness", by placing candles in their windows, to remember victims of genocide and unite against prejudice.
An outdoor campaign launched earlier this week to support the initiative. The campaign is being featured on Ocean Outdoor and JCDecaux sites across the UK.
Twitter developed an emoji for this year's HMD - a candle with a purple flame - and Royal Mail has used a special postmark this week.
Olivia Marks-Woldman OBE, chief executive of the Holocaust Memorial Day Trust, said: "As with everything else, we've had to change how we mark Holocaust Memorial Day this year. Our priority was to keep contributors, especially Holocaust survivors, safe.
"We are so grateful to everyone who made HMD happen this year: the government, celebrity readers, landmarks and billboards that lit up in purple – and to people across the UK who put candles in their windows. It has enabled everyone – despite the pandemic – to learn from genocide for a better future."