Their submissions portal is: http://harpervoyagersubmissions.com/.
Associate publicist Caroline Perny says —
While we’re always on the lookout for full-length fantasy, science fiction, and horror, we’re really in the market right now for Urban Fantasy and Military Sci-Fi. And be sure to check back throughout the year — we’ll be doing other calls for different genres as well!
Keep in mind we are looking for full length manuscripts between 60,000 and 90,000 words. The submission window closes on November 6th so get your manuscripts ready!