Formal name of the New START (for Strategic Arms Reduction Treaty) is " Measures for the Further Reduction and Limitation of Strategic Offensive Arms".
It’s a nuclear arms reduction treaty between the United States and the Russia, signed on April 8, 2010 in Prague.
Now after ratification from both the sides, the treaty has entered into force on February 5, 2011. The treaty is expected to last till 2021.
Though, the name is a follow up to START I, yet, the New START replaces the Treaty of Moscow (SORT), which was due to expire in December 2012. START-I was sealed in 1991 and expired in December 2009.
There was a proposed START II, which never came into force.
New START requires both sides to reduce their arsenal of warheads by roughly one-third of current levels – from 2,200 to 1,550.
Both sides are to monitor each other’s nuclear weapons stockpiles.