The annual festival started back in 1945.
Some people say it began as a food fight between a group of friends, others say people threw tomatoes at a carnival parade, and some believe it happened when tomatoes spilled from a truck.
This year the town will launch its first ever tomato-based obstacle course, the Tomatina race.

The two sides in the decades-old conflict have been holding peace talks since 2012.
The Northern Ireland delegation includes the Rev Harold Good, Sinn Fein's Paul Maskey, the DUP's Jeffrey Donaldson and the SDLP's Mark Durkan.
Two representatives from South Africa's ANC will also be attending.
The Northern Ireland delegation will share their experiences of the peace process, particularly the 1998 Good Friday Agreement.
Last month, Colombian President Juan Manuel Santos said that he had given his negotiating team instructions to resolve the outstanding issues before 23 March 2016.
Since starting official peace talks in Havana in November 2012, the two sides have struck deals on land reform, political participation, illegal drugs and now transitional justice.
However, none of these agreements will come into force until both sides put their signatures to the final agreement.
An estimated 220,000 people have been killed in the conflict since the 1960s, and more than five million internally displaced. About 8,000 left-wing Farc rebels continue fighting.
Rev Harold Good was one of two independent witnesses, the other being Fr Alec Reid, who oversaw the decommissioning of IRA weapons, a vital part of the peace process.
Mr Durkan said he was "delighted to share any insights or experiences I have had that could in any way help efforts to achieve peace in Colombia.
"Trade union and human rights groups have been engaging with people here on a cross-party basis for a number of years," he added.

Gao Yu, 71, was found guilty last April and challenged her conviction at a closed hearing in Beijing on Thursday.
The guilty verdict was upheld, but the jail term was cut from seven years to five and the medical grounds permitted.
Foreign governments and rights groups have condemned the guilty verdict, calling it politically motivated.
Sources have told the BBC that Ms Gao has already left prison.
The well-known investigative journalist was found guilty of sending an internal Communist Party document to Mingjing News, a Chinese-language website in the United States. The document warned against the dangers of a free press and an independent civil society.
At the time of the original conviction the court had said that Ms Gao had "illegally provided state secrets to foreigners".
Both Ms Gao and Mingjing News had denied she was the source of the leak.
However, on Thursday, Ms Gao confessed to the crime and expressed regret for her actions, and the appeals court reduced her sentence to five years and decided Ms Gao could "temporarily serve the sentence out of prison" as she was "severely ill", Chinese state media said.
Experts say Chinese courts often grant reduced sentences after convicts plead guilty. However, Ms Gao's lawyers told AP they continued to argue that she was innocent.
Many believe that Gao Yu is unpopular with the Chinese government because of her unrelenting reports focusing on China's elite-level politics, the BBC's Celia Hatton in Beijing reports.
Many people had pressed for a lighter sentence in consideration of Ms Gao's advanced age and her chronic heart problems.
Her son, Zhao Meng, had told the BBC he was concerned his mother would not survive another lengthy period in prison, her third since 1989.
Prominent human rights activist Hu Jia said (in Chinese): "I'm relieved Gao Yu can return to her own home, after a year and a half in custody... but the risk of being returned to jail at any time still hangs over Gao Yu's head, like the sword of Damocles."
More than 22,000 people from across the world have gathered in the small Spanish town of Bunol to celebrate the 70th annual Tomatina Festival by throwing 150 tonnes of squashed tomatoes at each other.
[NEXT_CONCEPT]
A delegation from Northern Ireland is travelling to Cuba  to provide support for peace talks between the Colombian government and the Farc rebel group.
[NEXT_CONCEPT]
A journalist jailed for leaking state secrets has been allowed to serve her sentence outside prison on medical grounds, Chinese media report.