Fox's Glee became famous for, among other things, its covers of well-known songs adapted into its high-school setting. The tunes became a huge part of the show's success, especially the mash-ups. A mash-up is a combination of two songs; at their best, mash-ups provide a fresh look into the individual songs while still creating something new and possibly groundbreaking.

RELATED: 10 Glee Musical Numbers That Have Aged Poorly

The show produced forty-five mash-ups, consolidating itself as the place for these unusual but welcome creations. And while some of these mash-ups received minimal attention, others became instant successes with fans and critics, cementing Glee as a television trailblazer.

Anything Goes/Anything You Can Do

Harmony smiling in Glee

Harmony was one of the Glee characters fans wanted to see more of but never did. Played by The Glee Project finalist Lindsay Pearce, Harmony was the lead singer of a rival show choir who only appeared in two episodes. However, she made a huge impression, thanks mainly to her amazing mash-up of "Anything Goes" and "Anything You Can Do."

Both songs are musical theater staples, so they are already iconic. However, joining them brings a new side to each, enhanced by Pearce's overwhelming voice. Her final note is incredible enough to make this mash-up memorable, but the tap interlude seals the deal.

Stop! In The Name Of Love/Free Your Mind

The ND boys performing at the choir room in Glee

The teams again prepare mash-ups for the second annual boys versus girls competition. Unlike season 1, where the girls' mash-up is undoubtedly superior, season 2 belongs to the boys' devastatingly charming combo of The Supremes' "Stop! In The Name of Love" and En Vogue's "Free Your Mind."

RELATED: 10 Songs Glee Would Do If It Was Still Airing (& Who Would Sing Them)

Looking sharp in blue tuxedos and echoing the Jersey Boys, the New Direction boys bring all the charm to their performance. Both songs fit surprisingly well together, and the pop-esque arrangement brings them directly into the 21st century.

Homeward Bound/Home

The New Directions' seniors performing on stage in Glee

There's no doubt Glee's main characters had several iconic scenes, but one of the sweetest and most emotional comes in the form of a mash-up. As the recently graduated characters reunite for Thanksgiving, they perform a mash-up of Simon & Garfunkel's "Homeward Bound" and Phillip Phillips' "Home."

Tender and full of nostalgia for the old days, the song captures the feelings of going back home after moving on from high school. Every singer gets their moment to shine, and their voices harmonize perfectly, delivering one of the most emotional moments in the show's history.

Survivor/I Will Survive

The Troubletones performing in Glee

The Troubletones were arguably McKinley's superior Glee Club. Led by Mercedes and Santana, the all-female group delivered sensational performances that perfectly blended killers vocals with elaborate dance sequences. For their Sectionals number, the Troubletones performed a mash-up of Gloria Gaynor's disco anthem "I Will Survive" with Destiny's Child empowering song "Survivor."

Without a doubt, "Survivor/I Will Survive" is one of the best Glee numbers performed at the auditorium. It's a true bop that uses both songs to their fullest, creating a true anthem of empowerment and self-love. It still stings that the Troubletones lost this contest, especially against the New Directions' sappy Michael Jackson tribute.

Thriller/Heads Will Roll

The ND and the football team performing on the field in Glee

Being the series that follows the Super Bowl is a daunting but privileged place that only a few select shows get. For the 2011 post-Super Bowl spot, Fox chose Glee, then at the peak of its influence and popularity. The episode, "The Sue Sylvester Shuffle," was something of a disappointment, but it did feature one of the show's most unforgettable mash-ups, "Thriller/Heads Will Roll."

Fans knew it was only a matter of time before Glee covered Michael Jackson's anthem, but no one expected the show to combine it with another song, least of all one as niche as the Yeah Yeah Yeah's "Heads Will Roll." However, the result is nearly-iconic, thanks largely to Kevin McHale and Naya Rivera's flawless vocals.

Halo/Walking On Sunshine

The girls performing Halo/Walking on Sunshine in Glee

"Vitamin D" was the show's first attempt at doing mash-ups, and it didn't disappoint. The episode follows Teri Schuester, acting as the school nurse, offering pseudoephedrine tablets to the kids while Will makes them compete against each other in a boys versus girls musical battle. The result is two overly energetic performances, but there's no denying the girls' number was superior.

Indeed, enhanced by Rachel and Mercedes' potent vocals, the girls' rendition of "Halo/Walking on Sunshine" is one of the best in the show's history. The storyline itself is deeply problematic and arguably one of the most cringeworthy moments in Glee, but the performance itself is amazing. Rachel's final note is enough to shame nearly every other of the show's mash-ups.

Anyway You Want It/Lovin' Touchin' Squzzin'

The New Directions performing on stage in Glee

"Journey" is undoubtedly the best episode from Glee's season 1. It features the New Directions competing in their first Regionals against Vocal Adrenaline. To honor their first-ever performance, Journey's "Don't Stop Believin'," the club performs a medley of the group's most famous songs, including a mash-up of "Anyway You Want It" and "Lovin' Touchin' Squezzin'."

The result is a catchy and energetic tune full of contagious energy. It's no wonder the audience at Regionals gets on their feet and puts their hands together. The choreography might be somewhat lacking, but the mash-up's vibe invites anyone that hears it to sing and dance like no one's watching.

I Feel Pretty/Unpretty

Quinn and Rachel singing at the choir room in Glee

Quinn is one of the Glee characters who got the short end of the writing stick. Her character arc was all over the place, but she received a complex and compelling storyline of acceptance and self-realization in late season 2. The episode "Born This Way" summarized her plot with an inspired mash-up of West Side Story's "I Feel Pretty" and TLC's "Unpretty."

The irony of both songs isn't lost on anyone, as Quinn and Rachel sing about the all-too-familiar struggle between inner and outer beauty. The mash-up is tender but deeply affecting, thought-provoking even, and the combination between Quinn's soft voice and Rachel's powerful belt enhance the song's strong emotions.

Singing In The Rain/Umbrella

The New Directions performing on the auditorium in Glee

One of the best things about Glee was how it introduced younger audiences to musical classics. From Cabaret to Carole King's Tapestry, the show featured several ageless songs throughout its run. However, combining the timeless classic "Singing in the Rain" with Rihanna's absurdly catchy 2007 hit "Umbrella" was a stroke of genius.

RELATED: 9 Songs The Glee Characters Should Have Performed, According To Reddit

Both songs complement each other nearly perfectly. Furthermore, Matthew Morrison and Gwyneth Paltrow's vocals fit the tunes like a glove, bridging classic Hollywood with a number 1 Billboard hit. The over-the-top performance, which included a rain machine, was the cherry on top of the elaborate cake.

Rumour Has It/Someone Like You

Mercedes and Santana looking sad while performing Rumour Hast It/Someone Like You

Since their debut, the Troubletones consolidated themselves as worthy opponents to the New Directions. Thanks to Mercedes and Santana's soaring vocals, the Troubletones became a serious threat, and their dominance became clear during their first confrontation against the New Directions.

Choosing to perform mash-ups, the Troubletones went with a combo of Adele songs. "Rumour Has It" and "Someone Like You" are incredible tunes by themselves, but no one expected them to go so well together. The mash-up is melancholic and unexpectedly angry, emotions enhanced by Amber Riley and Naya Rivera's soulful voices. "Rumour Has It/Someone Like You" ranks as Glee's best and most unforgettable mash-up, and every fan pretty much agrees.

NEXT: 10 Songs You Forgot Glee Covered