Hundreds of bonfires will be lit in Northern Ireland over the weekend - but why?
BBC News NI has tried to answer some of your questions.
Why do people light the bonfires now?
Bonfires are lit in unionist areas on 11 July to kick off the Twelfth celebrations.
They mark the Battle of the Boyne in 1690 when the Protestant William of Orange - also known as King Billy - defeated Catholic King James II.
Bonfires were lit to welcome - and guide - William of Orange.
Traditionally, nationalists have lit bonfires on 15 August to mark the Catholic feast of the Assumption, commemorating the Virgin Mary's death and assumption into heaven.
There have also been a small number on 8 August in nationalist areas to mark the anniversary of the introduction of internment - or detention without trial - on 9 August 1971.
What happens on the Twelfth?
Parades are held in many towns in Northern Ireland throughout the summer but the biggest event in the calendar is 12 July.
The Orange Order, which organises parades that attract thousands of people on 12 July, says the events are a way of expressing and promoting the Protestant culture and heritage.
The Twelfth isn't just celebrated in Northern Ireland - Protestants in the Republic of Ireland, New Zealand, Australia and the United States, to name a few, also celebrate it.
According to the Order, the core values of "Orangeism" include the promotion of the Protestant faith, maintaining the union between Great Britain and Northern Ireland, carrying out service to the Crown and delivering for the community.
However, many members of the predominantly Catholic nationalist community have said they view Orange marches as triumphalist and provocative.
Why are some bonfires so contentious?
Some people object to loyalist bonfires being used as a form of cultural expression, particularly when they involve the burning of flags, effigies and election posters.
Last year, Northern Ireland's then-First Minister Arlene Foster criticised people who placed "sectarian and offensive messages" on top of Eleventh Night bonfires.
I get trolled a lot, falsely accused of hating loyalists and unionists. Nothing could be further from the truth.— Naomi Long MLA (@naomi_long) July 4, 2021
I'd love to know what those people make of loyalists burning my image in an act of intimidation and blatant hatred.
Burning people's images isn't culture, folks. pic.twitter.com/6zAhrNDuPt
The bonfires can also raise tension if they are located close to nationalist areas.
There is also the issue of safety if bonfires are close to people and properties as well as their environmental impact.
Why are police concerned about some bonfires?
A bonfire close to an interface in north Belfast is probably the most contentious being examined by police, according to Chief Constable Simon Byrne.
Separately, the PSNI was present as contractors removed materials from a bonfire in east Belfast.
What is burnt at a bonfire?
Bonfires are largely constructed from wooden pallets and household waste, but old tyres are often placed in the centre to make the fire burn more effectively, subsequently releasing toxic fumes.
More eco-friendly beacons have been appearing around Northern Ireland in the last few years.
These are smaller, pyramid-shaped steel structures, which are pre-filled with a carbon neutral willow wood. They stand on a bed of sand to avoid damage to roads and surfaces, and are designed to be reusable.
Have bonfires always been this big?
No. Traditionally bonfires were much smaller but there were a lot more of them.
They were largely built on street corners or waste ground in loyalist areas.
But in recent years, communities have joined together to consolidate their resources to form much larger bonfires, often due to a lack of space.
Another reason for the increased size is a friendly rivalry between communities bidding to build the biggest bonfire.
Who pays for them?
Communities collect for bonfires months in advance - both financially and physically.
The Craigyhill bonfire in Larne, County Antrim, is aiming to be the biggest this year, and organisers say they raised £20,000 to pay for wooden pallets and a crane.
Some councils provide funding for Twelfth bonfires through cultural expression grants.
They come with stipulations such as not displaying paramilitary symbols or burning flags, effigies or tyres.
Why are some bonfires being lit this year before 11 July?
Bonfires are usually lit at midnight on 11 July - or sometimes earlier to allow more members of the community to attend and limit the noise and disturbance in the early hours of the morning.
Smaller children's bonfires and events, which often include bouncy castles, games and music, run earlier in the day near most bonfires.
As the Eleventh Night is a Sunday this year, most bonfires are being lit on Friday or Saturday night, as Sunday is a day of religious observance.