After most votes were counted, 60% voted no to Renzi's proposals and 40% voted yes. Voter turnout was 70%.
Even though Renzi claims his reforms would have reduced Italy's bureaucracy and made the country more competitive, many see the referendum as a way of Italians expressing their dissatisfaction with Renzi.
Much support of the 'no' side came from populist groups, such as the Five Star Movement, who hold anti-establishment sentiments.
The leader of the anti-immigrant Northern League, Mattaeo Salvin, said that the referendum was a "victory of the people against the strong powers of three-quarters of the world".
This Italian referendum follows the UK's Brexit, the rise of the anti-immigration group Front National in France, and the election of Donald Trump in the USA.
"The Italians have disavowed the EU and Renzi. We must listen to this thirst for freedom of nations," Marine Le Pen of France's Front National said on Twitter.
Once the results of the referendum were finalized, the Euro currency immediately fell against the USA dollar.
nationwide - throughout the whole nation; all of the people; the entire country
referendum - a vote by the people of a country to decide upon a specific issue
turnout - the amount of people participating
bureaucracy - the system of government where non-elected officials make decisions - ths is often onsidered as taxing and time-consuming
populist - an approach to government representing the interests of the common people
anti-establishment - going against the current and typical authority figures in the present government
sentiments - feelings (and thoughts) toward something