New York, NY Publishing giant Houghton Mifflin Harcourt is enjoying an impressive “growth spurt” at 3 Park Ave., even though it hasn’t as yet moved into Charles Cohen’s 41-story office tower. In its latest expansion move, the publishing house has taken an additional 10,500 s/f comprising a portion of the 23rd floor, bringing its total 3 Park Ave. headquarters footprint to over 100,000 s/f. Houghton Mifflin Harcourt, which expects to relocate from 215 Park Ave. South to its new home in the first quarter of 2016, began its “space odyssey” last December when it signed a 12-year, 35,000 s/f lease for the entire 19th and a portion of the 18th floor. Six months later, it added another 55,000 s/f by leasing the remainder of the 18th floor along with the entire 21st and 24th floors. “We’re delighted to have been able to accommodate the growing space requirements of this distinguished publishing house,” said Cohen, president and CEO of Cohen Brothers Realty Corp. According to Cohen, he has witnessed a strong leasing resurgence at his striking 600,000 s/f midtown skyscraper. Recent tenant arrivals have included Mimeo.com, Return Path, Inc., Cintra Software and Services, and Assouline, Inc. David Glassman and Joseph Cabrera of Colliers International represented Houghton Mifflin Harcourt in the latest long-term leasing transaction while Marc Horowitz, senior vice president and national director of office leasing at Cohen Brothers Realty Corp., represented the building owner. Situated between East 33rd and East 34th Sts., the class A skyscraper features a new lobby and elevator cabs designed by renowned architecture firm, FXFowle. The property, convenient to Grand Central Station and several major subway lines, is also home to an on-site New York Sports Club. Houghton Mifflin, headquartered in Boston, is one of the world’s longest-established publishing houses and largest providers of pre-K–12 education solutions. Among the other signature Manhattan office buildings owned and managed by Cohen Brothers are 623 Fifth Avenue, 135 East 57th Street, 805 Third Avenue, 750 Lexington Avenue, 622 Third Avenue, 3 East 54th Street, 475 Park Avenue South and the D&D Building at 979 Third Avenue.