Star Trek: Titan is a series of novels that take place after the events of the film Star Trek: Nemesis, detailing the adventures of the USS Titan under the command of Starfleet Captain William T. Riker. Riker was transferred from the Enterprise-E circa stardate 56844.9 (2379). Riker’s prior tours of duty comprised fifteen years as First Officer under Captain Jean-Luc Picard aboard the Enterprise-D and Enterprise-E. These novels are said to be a return to the ideal of exploration, a trademark of The Next Generation TV show. Though Riker’s assignment aboard the Titan is mentioned within Star Trek: Nemesis, the novels are not part of the Star Trek canon.

from the Star Trek Titan Wikipedia entry