Marchers included such notable names as the UN's General Secretary Ban Ki-Moon, former Vice President Al Gore, Primatologist Jane Goodall, and actor and activist Leonardo DiCaprio, who was recently named a Messenger of Peace.
We were there and asked the marchers we met along the way why they were.
People we talked to hailed from around the country and the world, and represented a diverse set of organizations and causes - but they held the common belief that addressing the issue of climate change will make the world a better place.
The People's Climate March comes two days before world leaders, including President Obama, are set to gather at the United Nations to address climate change, cut back on fossil fuels and invest in renewable energy.
"The idea is to make the biggest spectacle possible to tell leaders that bold, decisive action needs to take place," said Rosemary Dreger Carey, an environmental activist from Bergen County who is organizing New Jersey's turnout for the march.
WHAT DO health, beer, pizza, cars and computer chips have in common? Clean water. Whether you are drinking, fishing, swimming or manufacturing consumer goods, the world doesn't go around without clean water.
It's our source of life, the basis of a safe and sound society, as well as the foundation of healthy communities and a thriving economy. That is why the proposal by the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers to more clearly define the "Waters of the United States" is so important.