Seattle's King County Library System will go up against the New York Public Library on Tuesday to determine which one sorts books and other items faster.
On Tuesday morning, mechanized conveyor belts in both libraries will start rolling for one hour.
In New York, a multimillion-dollar unit dubbed the "Tin Man" sorts bar coded items.
KCLS was victorious in the initial competition in 2013.
At last year's contest, New York took the title by coming in with 12,570 in an hour - 702 more than the Seattle area crew. The two competitors are tied at 2-2.
The KCLS collection includes more than 4 million items, a total circulation of more than 21 million items in 2014, and more downloads of eBooks, Audiobooks and video - 2.3 million -than any other public library system in the country.
