Happy Sunday (Korean: 해피 선데이) is a Korean reality-variety show shown on the KBS2 network, which competes directly against MBC's Sunday Night and SBS's Good Sunday line-up. Although it has been broadcast since 2003, its line-up of shows has frequently changed, with a complete revamp occurring in Spring of 2007. At that time, three new shows were introduced – Are You Ready, High-Five, and Immortal Songs. Due to its poor reception, Are You Ready quickly evolved into 1 Night 2 Days, with most of its cast intact. In late November 2008, Happy Sunday had a revamp of its shows keeping 1 Night 2 Days as the second segment and bringing back Immortal Songs which was previously liked by viewers. However, in late March, Immortal Songs ended once again and was replaced with Qualifications of Men, making Happy Sunday an all-male cast, with a total of 14 members. In 2013, Qualifications of Men was cancelled and replaced with Star Family Show Mamma Mia. On November 3, 2013 Star Family Show Mamma Mia was moved to Wednesday nights and replaced with The Return of Superman.

Out of the three Sunday night shows, KBS's Happy Sunday, MBC's Sunday Sunday Night and SBS's Good Sunday, only KBS has kept its program as a "whole program". Both MBC and SBS has divided their Sunday night show into two parts, the first segment as one program and the second as another. Both MBC and SBS have done this to record better TV ratings, which is important in South Korean media to prove the show's popularity. The key variety programs which garner Sunday night ratings and are usually compared to one another are KBS Happy Sunday's 1 Night 2 Days, MBC Sunday Sunday Night's Real Men, and SBS Good Sunday's Running Man.

During the 1990s KBS2's Sunday program was called Super Sunday (슈퍼선데이). But in February 1998, the name was changed to Joyful Super Sunday TV (슈퍼 TV 일요일은 즐거워). In November 2003, the name was changed again to 101% Sunday (일요일은 101%). On September 13, 2004, voice (dubbing) artist and 2003 KBS Entertainment Awards Grand Prize (Daesang) winner, Jang Jeong-jin (장정진), was recording for The Lord of the Alley (골목의 제왕) segment where he had to eat rice cakes during a game and was later hospitalized. Because of this incident, Jang died a month later (October 11, 2004) due to necrosis ("brain death") and loss of oxygenation to the brain. The segment was abolished and since November 2004, the program has been renamed Happy Sunday.

In the segment 1 Night 2 Days (Korean: 1박2일), the members go on an overnight trip to various places of interest in Korea. The aim of the segment is to recommend holiday destinations to its viewers. Throughout the show, there are several mini-games played to see who will eat dinner (as opposed to a simple snack), who will do the chores or work that needs to be done, and who will sleep comfortably.

The show is enormously popular, that even its re-runs (which airs on the same night) has viewership ratings within the Top 20 Sunday night programs.

In the segment The Return of Superman (Korean: 슈퍼맨이 돌아왔다), celebrity fathers spend 48 hours with their children without their mothers.

Shoot-dori (means shooting kid, ko:날아라 슛돌이 / Nal Ah Ra Shoot-dori) is a variety show where a group of kids train and practice their football skills to compete with other mini-leagues. It is still airing, however at a different time slot and is no longer a part of Happy Sunday. This program now airs on the KBS N Sports channel. It is into its fourth season with a different cast.

K-1 fighter Choi Hong-man and celebrities participate in various physical challenges and games.