Ninja Sex Party (often abbreviated as NSP) is an American musical comedy rock duo consisting of singer Dan Avidan and keyboardist Brian Wecht. They formed in 2009 in New York City and are currently based in Los Angeles. They are also part of the musical trio Starbomb with friend and collaborator Arin Hanson.

The work of Ninja Sex Party typically consists of rock or synth-pop-oriented humorous songs, frequently on the topics of sex, seduction, love or fantasy, with Avidan and Wecht respectively portraying the characters of Danny Sexbang, an idiotic, exuberant, hypersexual Jewish man who tries to hit on women with varying degrees of success; and Ninja Brian, a non-verbal, extremely homicidal ninja with whom Danny is best friends.

To date, NSP has released nine studio albums (six consisting of original material, and four cover albums), in addition to four albums as a part of Starbomb. Their Under the Covers cover album series that began in 2016 saw them take on a non-comedic approach to music for the first time, covering various songs from the 1970s, 1980s and 1990s.

Wecht initially acted as record producer and performed all instrumentation on their early albums, until they started working with producer Jim Arsenault (and later Jim Roach) and backing band TWRP in 2015. Wecht and Avidan have appeared in TWRP's own works, either as individuals or as Ninja Sex Party. Since May 2018, Wecht also portrays Ninja Brian on his own live comedy show titled Ninja Brian's All-Star Variety Luau Spectacular. Every non-cover album that the group has released has reached #1 on the Comedy Albums chart, and their highest-peaking album on the Billboard 200 chart was #17 despite being independent.

Avidan, who previously sang in bands such as The Northern Hues and Skyhill, initially conceptualized the band. In need of a band member, Avidan was introduced to Wecht, who was the musical director of a comedy troupe in New York, by a mutual friend at the Upright Citizens Brigade Theatre, Julie Katz, a member of Wecht's comedy troupe (who would later be featured in their music video "The Decision"), to whom Avidan had asked if she knew any musicians. The band was formed in February/March 2009 with Avidan going by his stage-name/character "Danny Sexbang" and Wecht going by "Ninja Brian". However, the character "Danny Sexbang" was originally named "Danny Sweetnuts" before being changed to "Sexbang" as Avidan felt the name seemed "stronger."

Inspired by The Lonely Island and Flight of the Conchords, Ninja Sex Party is about "a Jewish superhero who wears a unitard, with his best friend who's a ninja, and together they sing songs about dicks, and try to hit [unsuccessfully] on women." The original goal of the project was to attempt to create a sitcom series similar to Flight of the Conchords.

They began performing together that summer, appearing in various film festivals, including SXSW, Dragon Con, and the LACS. They were awarded the "Trophy of Awesomeness" on Vimeo's video website. They won "Best Comedy Video Short" and "Best Comedy Song" in Improvisation News' 2010 INNY Awards. Their video "Sex Training" also appeared on the Comedy page of The Huffington Post. All their early music videos were directed, shot, and edited by Jim Turner, who was the only person paid for his involvement; all other people participating were friends working for free.

In 2011, they released their first album NSFW, which stands for Not Safe For Women on iTunes, which contained both original songs, and all of their previously released songs on YouTube.