Crowds at that time chanted, "Down with the Pahlavi monarchy! Down with [then Prime Minister Shahpour] Bakhtiyar!"
Faraj Sarkouhi, an exiled writer and journalist, says that for many Iranians, those were days of great hope in the country.
"I had been freed from jail in those days, and I hoped that the [revolutionary] forces would bring democracy and progress for the country, despite the religious leadership that caused some doubts, I hoped that the press would be free, the books would be published without censorship, [political] parties, associations and civil society organizations would be formed, and I hoped that I would be able to write freely. In fact, in these 25 years, I have not seen anything but the death and silencing of those beautiful hopes and dreams," Sarkouhi said.
Sarkouhi was a signatory to the 1994 Declaration of 134 Iranian Writers, a document that called for an end to literary censorship. He left Iran in 1998 after being jailed several times.
Many Iranians from different political groups and different backgrounds were involved in the protests that led to the fall of the Shah. They were united by strong opposition to the shah's rule, its lack of freedoms as well as foreign influence in the country.
The revolution itself was concluded 10 days after the return of Iran's main religious leader, Ayatollah Ruhollah Khomeini. Khomeini returned on 1 February 1979, after 14 years in exile -- lastly in France -- and took control of the revolution. "Independence, Freedom, and Islamic Republic" were the slogans of the revolution.
Ali Akbar Mahdi is a professor of sociology at Ohio Wesleyan University in the U.S. He says few people knew what an Islamic system would look like.
"The last [slogan, about the Islamic Republic] was really something that came out at the very end of the revolutionary process, when the leadership of the revolution was taken over by the clergy. And the public did not really know what the content of this Islamic Republic [would be]. They trusted one man, and that was Ayatollah Khomeini," Mahdi said.
On 1 April 1979, after a referendum, Khomeini declared the country an Islamic republic. Islamic laws were applied, and an Islamic constitution was created, which gave ultimate authority to unelected religious leaders.
Amir Taheri is a veteran Iranian journalist and writer who at the time of the revolution was editor in chief of Iran's largest newspaper, "Kayhan." He says the Islamic system dashed the hopes of many of the revolutionary forces.
"[It is,] of course, a disappointment to the left. It's a disappointment to the democrats and, of course, it was a disappointment to the monarchists, as well. So most of the hopes of the revolutionaries were dashed. Many of the leaders were executed by the mullahs when they came to power," Taheri said.
Saeed Rajayi Khorasani, a former Iranian ambassador to the UN, says the Islamic Revolution fulfilled all its promises -- Iran is an Islamic republic, Iran is independent, and there is a great deal of liberty in Iran. He was asked about the detention of writers and activists for expressing their views and the closure of more than 80 liberal publications in recent years.
"Of course, there are certain red lines in certain areas of, let's say, the political domain of the country. You cannot be disrespectful to the leadership. You cannot ignore the significance of the Shoraye Negahban, or the Council of Guardians. The Council of Guardians is also part of the constitution of the country," Khorasani said.
Analysts say the revolution has had mixed results.
Mahdi says the Islamization of Iran's judicial and system was one of the most devastating aspects of the revolution.
"The clerics did not like the shah's judicial system. They regarded it as modern, as civil and as Westernized, and they dismantled the whole thing from day one, and they put in place a Sharia law-based system, which has been very, very painful on the country, particularly on women in that country," Mahdi says.
Following the Islamic Revolution, wearing a veil became mandatory for women, and many other discriminatory laws were introduced, such as the need for a woman to first get permission from her father or husband before she could travel.
Mahdi says that after the revolution, Iranian women lost most of the rights they had gained during the shah's era, but says their social participation increased.
"Despite all that negativity, Iranian women's participation in social affairs and social life has increased tremendously because the traditional sector of the society -- which was the largest sector of society during the Pahlavi [period] -- did not participate because they never trusted the shah and the system, and they did not regard the society as a safe place for women. Now this kind of traditional fear, religious fear, has been removed, so there is a lot of gain there, as much as there is a great deal of suppression," Mahdi said.
Following the revolution, Iran became internationally isolated and mismanagement of the economy led to a sharp decline in living conditions.
The revolution has had some positive effects, but observers say they were largely inadvertent. Journalist Taheri says the revolution helped politicize Iranians and raise their political awareness. As a result, he says, Iranians now know what they want.
"The Iranian people now know that democracy and human rights are not abstractions, but they are concepts that affect their daily lives. So for the first time, there is a genuine popular constituency in Iran for democratization and the achievement of human rights. And I think that is really the most positive outcome of the past 25 years," Taheri said.
Today, state media reported that millions of people attended rallies around the country to reconfirm their allegiance to the 1979 revolution. In the capital, Tehran, tens of thousands reportedly marched to Azadi (Freedom) Square to take part in a parade.
But the celebrations have been overshadowed by the political crisis over the disqualification of more than 2,000 pro-reform candidates from this month's parliamentary elections.
Iranian President Mohammad Khatami today used the anniversary to deliver a speech to a crowd in Azadi Square, in which he warned that restricting political freedoms represents a threat to the nation. Khatami reminded the crowd of what motivated the revolutionaries of a quarter century ago.
"A quarter of a century has passed since the victory of the Islamic revolution. Before the victory of the revolution, this public square, in which you have gathered today, saw masses of people who, based on Islam, chanted for independence and freedom," Khatami said.
Khatami, elected as a reformer, said elections are a symbol of democracy and warned that "if this [right] is restricted, it's a threat to the nation and the system."
Most of Iran's young people have few, if any, memories of the revolution. Ali was born one year after the revolution and says it has brought nothing but "hardship and humiliation." He also says he will not vote in this month's elections.
"I don't think my vote will make any difference. This year, most of the reformist candidates have been disqualified, but even when they had the majority in the parliament, all their bills were rejected by the Guardians Council. [As long as] the Guardians Council is in power, elections are useless," Khatami said.
Professor Mahdi says most Iranians aspire for change but don't want another revolution.
"The Islamic Republic is in a struggle with itself. There is a tremendous amount of force within the country and a great deal of aspiration to change, but this change is desired to be gradual and nonviolent. Iranians do not seem to be at this stage anymore, desiring some kind of a violent overthrow again, just like the revolution, because they did not have much positive experience out of that revolution. So for that reason, I believe that we will see more change, more opening of the system and more pressure from the bottom," Mahdi said.