Secretly, Greatly (Korean: 은밀하게 위대하게; Hanja: 隱密하게 偉大하게; RR: Eunmilhage Widaehage; MR: Ŭnmirhage Widaehage) is a 2013 South Korean action comedy-drama film starring Kim Soo-hyun, Park Ki-woong, and Lee Hyun-woo, who play North Korean spies who infiltrate South Korea as a village idiot, a rock musician, and a high school student, respectively. They assimilate to small-town life while awaiting their orders, until one day, due to a sudden power shift in the North, their mission turns out to be an order to commit suicide.

The film is based on the 2010 spy webtoon series Covertness by Hun, which has received over 40 million page hits. Upon its release on June 5, 2013, the film broke several box office records in South Korea: the highest single day opening for a domestic film, most tickets sold in one day for a domestic film, the biggest opening weekend, the highest-grossing webtoon-based film, and the fastest movie to reach the million, two million, three million, and four million marks in audience number. Movie pundits attribute its success to a large percentage of teen audience turnout.