The song is originally based on a Polish lullaby, "Wlazł kotek na płotek" ("The kitten climbed the fence"). The lyrics were noted by folklorist Oskar Kolberg in 1837, and the tune was first published by Stanisław Moniuszko in 1849, based on a Polish folksong. Władysław Syrokomla and Wiktor Każyński published a version of this song in 1857, in Pieśniach ludu polskiego ("Songs of the Polish people").
In December 2015, the heirs of Edith Newlin filed a lawsuit against the various companies associated with The Big Bang Theory, claiming that the words and music to the song appeared in the book Songs for the Nursery School published in 1937 by Willis Music Company, based on a poem by Newlin; the copyright to the book was renewed in 1964.
The website for Willis Music states:
The suit by Newlin's daughters, on the other hand, claimed that they held the copyright. Furthermore, they alleged that they did not authorize the use of the lyrics, that Willis Music did not have permission to authorize others to use the lyrics, and that the lyrics had been used not only in the television series but on various kinds of program-associated merchandise without proper permission.
Seidman, Robert (November 16, 2010). "CBS.com Launches "Soft Kitty" Contest Inspired by Popular Song From CBS Hit 'The Big Bang Theory'". TV by the Numbers. Archived from the original on November 19, 2010. Retrieved August 4, 2013. https://web.archive.org/web/20101119093338/http://tvbythenumbers.zap2it.com/2010/11/16/cbs-com-launches-soft-kitty-contest-inspired-by-popular-song-from-cbs-hit-the-big-bang-theory/72269
Newmeister, Larry (December 28, 2015). "Late Teacher's Heirs Sue Producers of 'The Big Bang Theory,' Alleging Copyright Infringement". U.S. News & World Report (online ed.). Archived from the original on March 3, 2020. Retrieved December 28, 2015. {{cite journal}}: Unknown parameter |agency= ignored (help) https://www.usnews.com/news/entertainment/articles/2015-12-28/heirs-to-new-hampshire-poet-sue-big-bang-theory-producers
Padnani, Amisha (December 29, 2015). "'Big Bang Theory' Is Accused of Stealing 'Soft Kitty' Lyrics". The New York Times (online ed.). Archived from the original on April 17, 2021. Retrieved December 29, 2015. /wiki/Amy_Padnani
McCartney, Laura Pendleton (Ed.) (1937). Songs for the Nursery School (Imperial 662 ed.). Cincinnati, OH, US: Willis Music Company. p. 21. OCLC 1024186. Retrieved August 3, 2013. http://www.nla.gov.au/apps/doview/nla.mus-vn2628642-p
"Chase v. Warner Bros. Entm't, Inc., 247 F. Supp. 3d 421 | Casetext Search + Citator". casetext.com. Retrieved April 8, 2022. https://casetext.com/case/chase-v-warner-bros-entmt-inc
McCarthy, Tyler (February 2018). "'Young Sheldon' reveals the origin story of the 'Soft Kitty' song". Foxnews.com. Fox News. Archived from the original on February 2, 2018. Retrieved February 2, 2018. https://www.foxnews.com/entertainment/young-sheldon-reveals-the-origin-story-of-the-soft-kitty-song/
"Young Sheldon Confirms Sheldon's Callous TBBT Soft Kitty Lie To Penny". MSN.com. Retrieved May 1, 2023. https://www.msn.com/en-us/tv/news/young-sheldon-confirms-sheldon-s-callous-tbbt-soft-kitty-lie-to-penny/ar-AA18tHUq
"Wlazł kotek na płotek". Biblioteka Polskiej Piosenki. Retrieved May 1, 2023. https://bibliotekapiosenki.pl/utwory/Wlazl_kotek_na_plotek
Bowden, Ebony (December 30, 2015). "The Big Bang Theory sued amid claims show 'wilfully' stole poem 'Soft Kitty'". The Sydney Morning Herald. Archived from the original on December 31, 2015. Retrieved August 18, 2021. http://www.smh.com.au/entertainment/comedy/the-big-bang-theory-sued-amid-claims-show-wilfully-stole-poem-soft-kitty-20151230-glwl20.html
Burlingame, Ross (December 28, 2015). "The Big Bang Theory Getting Sued Over Soft Kitty Song". ComicBook.com. Archived from the original on August 18, 2021. Retrieved August 18, 2021 – via Yahoo Entertainment. https://www.yahoo.com/entertainment/big-bang-theory-getting-sued-030924675.html
Bowden, Ebony (December 30, 2015). "The Big Bang Theory sued amid claims show 'wilfully' stole poem 'Soft Kitty'". The Sydney Morning Herald. Archived from the original on December 31, 2015. Retrieved August 18, 2021. http://www.smh.com.au/entertainment/comedy/the-big-bang-theory-sued-amid-claims-show-wilfully-stole-poem-soft-kitty-20151230-glwl20.html
The Australian Broadcasting Corporation (1993). The Best of Play School (Liner notes). Australia: ABC Music, EMI. 724381434321. (Note: Track #34) /wiki/Australian_Broadcasting_Corporation
Bowden, Ebony (December 30, 2015). "The Big Bang Theory sued amid claims show 'wilfully' stole poem 'Soft Kitty'". The Sydney Morning Herald. Archived from the original on December 31, 2015. Retrieved August 18, 2021. http://www.smh.com.au/entertainment/comedy/the-big-bang-theory-sued-amid-claims-show-wilfully-stole-poem-soft-kitty-20151230-glwl20.html
Chase, et al. v. Warner Bros. Entertainment Inc., et al., No. 15-10063 (S.D.N.Y. filed December 28, 2015). https://archive.org/details/gov.uscourts.nysd.451633
McCartney, Laura Pendleton (Ed.) (1937). Songs for the Nursery School (Imperial 662 ed.). Cincinnati, OH, US: Willis Music Company. p. 21. OCLC 1024186. Retrieved August 3, 2013. http://www.nla.gov.au/apps/doview/nla.mus-vn2628642-p
Newmeister, Larry (December 28, 2015). "Late Teacher's Heirs Sue Producers of 'The Big Bang Theory,' Alleging Copyright Infringement". U.S. News & World Report (online ed.). Archived from the original on March 3, 2020. Retrieved December 28, 2015. {{cite journal}}: Unknown parameter |agency= ignored (help) https://www.usnews.com/news/entertainment/articles/2015-12-28/heirs-to-new-hampshire-poet-sue-big-bang-theory-producers
Padnani, Amisha (December 29, 2015). "'Big Bang Theory' Is Accused of Stealing 'Soft Kitty' Lyrics". The New York Times (online ed.). Archived from the original on April 17, 2021. Retrieved December 29, 2015. /wiki/Amy_Padnani
"Music: January–June 1964". Catalog of Copyright Entries: Third Series, Volume 18, Part 5, Number 1. Washington: Copyright Office — The Library of Congress. 1966. p. 829. LCCN 06035347. Archived from the original on March 1, 2022. Retrieved December 4, 2020. Songs for the Nursery School; w & m Laura Pendleton MacCarteney, illus. by Peter Perrine. 21 June 1937; EP65337. Laura Pendleton MacCarteney (A); 22 Jun 1964; R339640 https://books.google.com/books?id=DzEhAQAAIAAJ&q=%22Songs+for+the+Nursery+School%22&pg=PA829
"Soft Kitty - Where does it come from?". Willis Music. May 5, 2015. Archived from the original on January 1, 2016. Retrieved January 1, 2016. http://willismusic.com/soft-kitty/
Newmeister, Larry (December 28, 2015). "Late Teacher's Heirs Sue Producers of 'The Big Bang Theory,' Alleging Copyright Infringement". U.S. News & World Report (online ed.). Archived from the original on March 3, 2020. Retrieved December 28, 2015. {{cite journal}}: Unknown parameter |agency= ignored (help) https://www.usnews.com/news/entertainment/articles/2015-12-28/heirs-to-new-hampshire-poet-sue-big-bang-theory-producers
Stempel, Jonathan (March 29, 2017). "Lawsuit claiming 'Big Bang Theory' stole 'Soft Kitty' is dismissed". Reuters (online ed.). Archived from the original on November 12, 2020. Retrieved April 13, 2017. https://www.reuters.com/article/us-television-bigbangtheory-idUSKBN170304
"Chase v. Warner Bros. Entm't, Inc., 247 F. Supp. 3d 421 | Casetext Search + Citator". casetext.com. Retrieved April 8, 2022. https://casetext.com/case/chase-v-warner-bros-entmt-inc