First of all, it is important to define the three main elements in order to define the public debt sustainability. The first key word is the public debt, which represents the total amount of all the credits that Greece contracted and has to pay in the future. The amount of Greece's public debt stands at about 300 billion euros in 2010. Then, the public deficit is a different notion but in relation with the public debt, and this amount means for a particular country, in that case for Greece, the difference between the revenues and the expenditures. The amount of the Greek public deficit is of 10.99% in 2010 of the GDP. (356 796 billion of dollars) The sustainability is a very important word but however it's an imprecise concept. It can be regarded at short, medium or long term concept, with the open question of how to define the horizons, and debt and deficits can be measured gross or net, including or excluding the liabilities of social security systems and other items.