Groups and groups of cannabis users gather every year to celebrate together for the festival.
Today marks 420 Day - a chance for cannabis users to gather for the annual drug festival and celebrate together.
But what exactly is it?
The annual festival sees hundreds of cannabis smokers gather in parks and venues, with huge events taking place in both Manchester and London in recent years.
Around 500 people went to Manchester's Platt Fields Park festival last year - with police on patrol making no arrests despite participants openly smoking cannabis.
There was also an event in London's Hyde Park.
Here we take a look at exactly where it all started:
What is 420?
The phrase 420 - pronounced ‘four twenty’ – has become a well-known term in cannabis culture.
It refers, quite literally, to the date the festival takes place on every year - as smokers gather at 4.20pm.
Where did it start?
A group of pot-smoking students in California, known as the Waldos, coined the name while searching for an abandoned crop of marijuana in 1971.
An international day of pro-cannabis events is now held every year on April 2TH0 as a nod to the term.
The global protest calls for governments around the world to decriminalise cannabis as a harmful drug.
Cannabis was re-classified as a lower category Class C drug under Tony Blair 's government in 2004 but was later returned to its Class B status under Gordon Brown.
How and where can you celebrate 420?
here are separate events taking place across the country every April 20 at 4.20pm.
Each one sees hundreds of people gather, before smoking together during the afternoon to mark the date and show a united front in the on-going protest.
Despite a visible police presence at 2014’s events, no arrests were made, with the event passing off peacefully.
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