A 'yes' vote means staying with the European Union.
With a combined population of over 500 million inhabitants, or 7.3% of the world population, the EU in 2014 generated a nominal gross domestic product (GDP) of 18.495 trillion US dollars, constituting approximately 24% of global nominal GDP and 17% when measured in terms of purchasing power parity. As of 2014 the EU has the largest economy in the world, generating a GDP bigger than any other economic union or country. Additionally, 26 out of 28 EU countries have a very high Human Development Index, according to the UNDP. In 2012, the EU was awarded the Nobel Peace Prize.(From Wikipedia, the free encyclopedia)
Mr Tsipras urged voters to reject the "sirens of scaremongering", but added that: "Whatever we choose... Come Monday we are all together."
However, Mr Tsipras faces vocal opposition at home - with opposition leader Antonis Samaras calling on "every Greek man and every Greek woman above and beyond parties" to vote "Yes", along with several deputies from Syriza's own coalition partner, the Independent Greeks.