With analysts predicting a tight race that will decisively impact the country's future, here are a selection of voices from both sides of the divide.
- 'Yes' -
-- 'Erdogan for a strong Turkey'
"Because we want Turkey to grow, because we want Recep Tayyip Erdogan to remain our leader, without him Turkey is not herself. We want to show that we are behind him," Nahil Unal, a 'Yes' supporter, said at Erdogan's giant rally in Istanbul on Saturday.
-- 'Standing up to foreign powers'
"For the future of our children, for Turkey to be independent again, we are here. Right now Turkey is not independent. The countries of the world are attacking us. From one side the Netherlands, from the other side the USA, France, Germany, Russia and even our neighbours," said Ihsan Eksi.
-- 'Worthy successor of Ottomans'
"He has a lion's heart. We know that he will defend Turkey like nobody before him," 48-year-old Metin Kaya said in Erdogan's home district of Kasimpasa.
"Europe has been scared of us since the Ottoman Empire and our history is our honour which is being repeated today. That's why (Europe) they are trying to intimidate us. Erdogan is the worthy grandson of Fatih," he said referring to the Ottoman Sultan Fatih, the conqueror who seized Istanbul from the Byzantines.
-- 'He loves this nation'
"I watch almost all the speeches of the president. When you hear him you see that he sincerely loves this nation. No, I don't find him too aggressive. He defends us, it's normal, he's our leader," said Mesut Can, 49, a grocery store owner from the Istanbul district of Gaziosmanpasa.
- 'No' -
-- 'No to one man rule'
"We say 'No', to have a more democratic system, so that we can remain in a democratic, parliamentary system, to say 'No' to a man who alone would lead a country of 80 million people," Saim Akbulut said at the pro-Kurdish HDP's Ankara rally on Sunday.
-- 'Changes not helpful for future'
"...why am I saying 'No'? And why are these women saying 'No'? It's because there is not even one article in this text about women, nothing for children, it's because we are against a regime led by just one man," Burcu Zeybek, a female opposition CHP activist, said.
-- 'Against further polarisation'
"He is already performing his current duties without recognising the law. It is nonsense to further polarise the country!" said Sukru Yalcin, rallying near a 'No' tent in the historic Eminonu square in Istanbul. "We are saying that it does not suit 80 million to be governed by one man's thinking."
-- 'Yes won't help Kurdish areas'
"They come to us and want 'Yes'. We have no reason to say 'Yes.' Why 'Yes'? They say it's for peace. Then what's your project?" said Halil Uysal, in his 30s and from the Kurdish majority province of Diyarbakir, in the conflict-torn southeast. "They say 'Yes' for development. Then what's your project? Nothing."