The book tentatively titled "Leonard: A 50 Year Friendship," is expected to hit bookstores next year via St. Martin's Press, reported The Wrap.
Shatner, 84, and Nimoy respectively played Captain Kirk and Mr Spock on the original "Star Trek" series, giving both the actors incredible fame.
They came up together in Hollywood and the Golden Globe Award-winning actor has a unique perspective on Nimoy, who died earlier this year.
He is also with Nimoy's family including his son, Adam Nimoy.
He has also interviewed several key figures from Nimoy's past.