25 Grey's Anatomy Episodes You Must Watch Before Season 10

This fall, Grey's Anatomykicks off its 10th season — which will include its momentous 200th episode — and TVGuide.com has compiled the best episodes that fans and new viewers alike must watch (or re-watch!) before diving back in.

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Through the death (George! Lexie!), heartbreak (Denny! Izzie!) and weddings (yay for post-its!), executive producer Shonda Rhimes, her team of writers and the talented cast and crew have taken all of us on an amazing journey. Check out a countdown of our top 25 episodes below:

 25. "Song Beneath the Song" — Season 7, Episode 18
What happened: After Callie (Sara Ramirez) and Arizona (Jessica Capshaw) get into a major car crash, a semi-comatose Callie envisions herself and her colleagues singing as they try to treat her extensive injuries. After the cast performs songs — no jazz hands, thankfully! — made famous by the series, like "Chasing Cars" and "Breathe (2AM)," Callie wakes up and proposes to Arizona.
Why it was a game-changer: The musical episode may not have been everyone's favorite, but Rhimes, decided to take a risk similar to Buffy the Vampire Slayer, one of her favorite series, and try something new. Not only that, but it lead to Callie and Arizona's wedding, which — while not the first lesbian nuptials on broadcast television — was certainly a momentous occasion. 

24. "The Other Side of This Life Parts 1 and 2" — Season 3, Episode 22 and 23
What happened: The two-hour episode serves as a backdoor pilot for Private Practice, which sees Addison (Kate Walsh) venture to Los Angeles to reunite with old friends Naomi (played by Merrin Dungey, later replaced by Audra McDonald) and Sam (Taye Diggs) in hopes of enlisting their help to get pregnant. It also marksthe episode where Thatcher Grey's (Jeff Perry) wife Susan (Mare Winningham) dies essentially from hiccups.
Why it was a game-changer: It was the beginning of the end for Addison Montgomery at Seattle Grace, and the start of a series that spanned six seasons, putting Rhimes into a rare group of showrunners with multiple shows on the air and providing opportunities for crossovers.

23. "If/Then" — Season 8, Episode 13
What happened: Meredith (Ellen Pompeo) dreams of a world in which her mother Ellis Grey (Kate Burton) never got Alzheimer's and went on to become the Chief of Seattle Grace. In this alternate reality, Meredith is bright and shiny and dating Alex (Justin Chambers), who is cheating on her with April (Sarah Drew). Meredith and Cristina (Sandra Oh) are enemies, and Owen (Kevin McKidd) and Callie are unhappily married. Meanwhile, Addison and Derek (Patrick Dempsey) are still together, while Lexie (Chyler Leigh) has become a drug addict.  
Why it was a game-changer: Even though most of our favorite couples were separated in the alt-reality, by the end of the hour, there was some spark between each of them that insinuated they were all truly meant to be even in this reality, like when Meredith and Derek met up at Joe's bar at the end. 

22. "Moment of Truth" — Season 8, Episode 21
What happened: Our favorite residents, whose careers we've mostly been following since the beginning of the series, head to San Franciscoto take the oral boards. But April scores better in life than on her test — which she ultimately fails — after she loses her virginity to best friend Jackson (Jesse Williams) while on the trip.
Why it was a game-changer: "Virgin Mary" April Kepner finally lost her virginity, which kicked off a fun new relationship for Grey's fans to root for. Sorry, Intern Stephanie (Jerrika Hinton)!

21. "The Time Warp" — Season 6, Episode 15
What happened: The series takes a trip down memory lane to see a younger Ellis Grey (Sarah Paulson) and Richard Webber (J. August Richards) at the height of their affair. We also learn that in her pre-Nazi days, Bailey (Chandra Wilson) goes by the name Mandy and is a much meeker version of herself until the Chief (James Pickens Jr.) gives her a boost of confidence. Additionally, we find out Callie and Alex slept together in her early days at Seattle Grace.  
Why it was a game-changer: It was an eye-opening experience to watch both Ellis and Richard attempt to break through as doctors at Seattle Grace when women and African-Americans were treated very poorly in the workplace.

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20. "Who's Zoomin' Who?" — Season 1, Episode 9
What happened: The episode has its funny moments after a number of our favorite interns are diagnosed with Syphilis, but the real drama comes with the surprise arrival of Addison Montgomery Shepherd. That's right, McDreamy is married!
Why it was a game-changer: Fans had been rooting for MerDer from the beginning of the series, never even realizing that he was already hitched. The shocking cliff-hanger in the Season 1 catapulted the series into its superb second season, when the Grey's fandom really took off.

19. "Unaccompanied Minor" — Season 7, Episode 22
What happened: Meredith's misdeed in tampering with the Alzheimer's clinical trial comes to light, ending with her suspension. Derek also tells her he can't raise a child — the newly adopted Zola — with someone who would ruin his trial. Meanwhile, Cristina discovers she's pregnant, but plans to get an abortion, causing a huge divide in her relationship with Owen. Additionally, Teddy (Kim Raver) admits her love for Henry (Scott Foley), while Mark (Eric Dane) does the same for Lexie, but she says he needs to let her go so she can fully be with Jackson.
Why it was a game-changer: It was the first of many falling dominoes in the Cristina and Owen relationship that eventually led to the couple's demise.

18. "Dark Was the Night" — Season 8, Episode 9
What happened: When Henry is brought into the hospital vomiting blood, Teddy has Cristina unwittingly operate on him. It's only after Cristina calls time of death that she finds out she was operating on her mentor's husband. This is also the episode where Meredith and Alex's ambulance is struck by a car on the side of the road.
Why it was a game-changer: It really marked the beginning of the end of Teddy's time at Seattle Grace. She stuck around until the end of the season, but her relationship with Cristina was never the same after that.

17. "Invasion" — Season 6, Episode 5
What happened: We first meet the invading residents from Mercy West, including April, Jackson, Reed (Nora Zehetner) and Percy (Robert Baker). Unfortunately, Percy uses Izzie (Katherine Heigl) to get ahead, leading her to make an irreparable mistake that costs Izzie her job. In the end, she leaves Seattle Grace and Alex, thinking he had a hand in her firing. The episode also marks the return of Callie's father, Carlos Torres (Hector Elizondo), who doesn't approve of her relationship with Arizona until she delivers the landmark "good man in a storm" speech.  
Why it was a game-changer: The infusion of residents offered up a wealth of new story lines. Additionally, Izzie's exit — so Heigl could film a movie — opened up the door for fans to see what Grey's would be like without her on a more permanent basis.

16. "Life During Wartime" — Season 5, Episode 6 
What happened: Owen Hunt returns to Seattle Grace full-time, even though his unconventional methods rub most of the staff the wrong way. After Hahn (Brooke Smith) and Callie sleep together, Hahn has the "I see leaves" realization that she is "so, so, so gay," which ultimately leads to the end of their relationship as Callie was still discovering who she is.
Why it was a game-changer: Owen's return really kicked off the start of his relationship with Cristina, while Callie began a new journey of self-discovery that eventually leads her to Arizona.

15. "A Change Is Gonna Come" — Season 4, Episode 1
What happened: After her failed wedding to Burke (Isaiah Washington), Cristina and Meredith return from the honeymoon to find that Burke has permanently left the hospital. Meredith also gets a shock when she finds out that her half-sister Lexie Grey is now an intern at Seattle Grace alongside George, who is repeating his intern year after failing his exams.
Why it was a game-changer: The introduction of Lexie Grey brought out an entirely new side in Meredith as she struggled with vulnerability and her attempts to shut her sister out. And even though Meredith didn't immediately jump on the bandwagon, we certainly fell in love with Little Grey from the start.

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14. "Some Kind of Miracle" — Season 3, Episode 17
What happened: The third of a three-part arc that features the ferry boat crash sees Meredith stuck in a semi-comatose limbo alongside deceased former acquaintances, including Dylan (Kyle Chandler) and Denny (Jeffrey Dean Morgan), who try to convince her to head back to her life. After her mother Ellis dies, the two meet briefly as Ellis tells her she's anything but ordinary. Once Mer wakes, Cristina is by her side to tell her person about the engagement to Burke.
Why it was a game-changer: Meredith finally got the acceptance from her mother that she so desperately needed to be able to move on with her life. And seriously, who didn't cry during this moment?

13. "Things We Said Today" — Season 9, Episode 10
What happened: Even though Bailey should be on the way to her wedding to Ben (Jason George), she rushes to the hospital to try to save Adele's (Loretta Devine) life. When Webber later shows up to the wedding, he reveals to Meredith that Adele ultimately died. Additionally, Arizona wants to try to have sex for the first time since the plane crash. Though she and Callie don't do it until later in the season, Callie promises not to leave her. Meanwhile, Alex and Jo (Camilla Luddington) begin bonding over their mutual rough upbringing.
Why it was a game-changer: Though someviewers weren't a fan of Jo, this marked the beginning of her bond with Alex that eventually leads to a new relationship that will hopefully last for Alex, who hasn't had the best luck when it comes to women. (Izzie, Ava, Lucy and Addison, to name a few.)

12. "Remember the Time" — Season 9, Episode 2
What happened: The plane crash survivors deal with PTSD, including Cristina being unable to speak until she runs away from Seattle Grace. Arizona fears she'll lose her leg and makes Callie promise they won't amputate. Mark begins to feel better, but realizes that he is feeling a "surge," the last bit of energy before a terminally ill patient dies.
Why it was a game-changer: Season 9 kicked off with an episode that jumped ahead months after the crash, so viewers didn't learn what happened out in the woods until this episode. It helped most fans deal with the loss of Mark and even Lexie, whom everyone had mourned all summer.

11. "Start Me Up" — Season 7, Episode 12
What happened: Arizona returns from Africa only to discover that Callie is pregnant with Mark's baby. Elsewhere, the residents must teach med students, who will go on to evaluate them, and Teddy must make life-changing decisions for Henry since she is his legal spouse.
Why it was a game-changer: What seemed like a filler episode in the middle of the season came with the jaw-dropping reveal that would forever change the Callie-Arizona-Mark dynamic.

10. "Elevator Love Letter" — Season 5, Episode 19
What happened: After Izzie's brain tumor surgery is successful — remember when she had cancer? — Derek plasters the walls of a Seattle Grace elevator with the scans of all the successful surgeries he's had with Meredith before proposing to her. This was also the episode where Owen's PTSD gets the best of him and he chokes Cristina in the middle of the night.
Why it was a game-changer: It was a moment five seasons in the making as fans endured the many MerDer breakups and makeups.

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9. "Perfect Storm" — Season 9, Episode 24
What happened: Thanks to a super storm, the newly renamed Grey-Sloan Memorial Hospital suffers from a power outage, which is a perfect time for Meredith to go into labor, right? Because of her earlier fall down the stairs, she suffers complications and must have a C-section in the dark. But Bailey saves her life and they name the baby after her. Meanwhile, Callie discovers that Arizona cheated with Dr. Boswell (Hilarie Burton), Alex admits he loves Jo, Cristina calls things off with Owen, April tells Jackson to give her a reason not to marry Matthew (Justin Bruening), and Webber is last seen apparently lifeless after being electrocuted by the generators.
Why it was a game-changer: The rock of the hospital could actually die, isn't that enough? The finale also left many fan factions torn up over the realization that their favorite couples could really be calling it quits.

8. "Didn't We Almost Have It All?" — Season 3, Episode 25
What happened: Cristina gets stressed over her impending nuptials to Burke, who realizes that she'll never be ready to get married, so he leaves her — and Seattle Grace — for good. Derek admits to Meredith that he met a girl at the bar — it turns out that was Meredith's sister Lexie Grey, who will be a new intern at the hospital! — and they end up calling it quits once again because Derek feels he's being taken for granted.
Why it was a game-changer: Cristina being left at the altar facilitated Isaiah Washington's exit from the series. It also helped cement who Cristina is: Work will always come before love.

7.  "Losing My Religion" — Season 2, Episode 27
What happened: Denny finally gets his heart and even proposes to Izzie, but dies before his fiancée returns to the hospital. Izzie admits to being the one responsible for cutting Denny's LVAD wire and quits her job. Elsewhere, Meredith ditches her prom date — the prom was for Webber's sick niece, remember? — Finn (Chris O'Donnell) and has passionate sex with Derek at the hospital.
Why it was a game-changer: No one will forget the image of Izzie in her pink prom dress arriving at the hospital only to find that her new fiancé is dead.

6. "Make Me Lose Control" — Season 2, Episode 3 
What happened: Although Meredith has been hiding that her mother has Alzheimer's, Ellis Grey is brought into Seattle Grace, where she is treated by George, whom she thinks is her ex-husband Thatcher Grey. Elsewhere, Cristina collapses in the OR after having an ectopic pregnancy. Her baby with Burke is then aborted.
Why it was a game-changer: Everyone discovered the extra stress Meredith had been dealing with as her famed surgeon mother's mind had been deteriorating.

5. "Flight" — Season 8, Episode 24
What happened: After their plane to Boise crashes in the woods, Lexie quickly dies from her injuries sustained during the crash, but not before Mark tells her he loves her. Derek's hand is crushed, Arizona's leg is broken, and Mark nearly dies as well. Back in Seattle, Teddy takes an offer to leave the hospital.
Why it was a game-changer: Lexie's death was shocking and heartbreaking, especially after Mark's confession. But the finale also left the fate of the rest of the doctors up in the air as they hadn't been rescued when the season ended.

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4. "As We Know It" — Season 2, Episode 16
What happened: Meredith was forced to shove her hand into the cavity of a man with an unexploded ordinance — aka there was a bomb in the hospital! They finally remove the explosive from the patient, and Dylan takes it out into the hallway, but it explodes, showering Mer with pink mist. Elsewhere, Bailey refuses to give birth without her husband (Cress Williams) by her side, who is undergoing surgery elsewhere in the hospital. George helps her through the delivery, which is why Tuck's middle name is George.
Why it was a game-changer: It was a turning point for Meredith to witness such horrific death first hand, but it also helped begin a healing process between her and Derek after she couldn't remember what their last kiss was like in the wake of such tragedy. The episode also landed both Rhimes and Chandler Emmy nominations.

3. "A Hard Day's Night" — Season 1, Episode 1
What happened: It's the interns' very first shift at Seattle Grace, where Meredith finds a new ally in Cristina and also realizes that she had a one-night stand with her new boss Derek. We also meet fellow interns Izzie, the model, Alex, the jerk and George, whose first failure in the OR lands him with the nickname 007.
Why it was a game-changer: The Fab Five — Alex, Meredith, Cristina, Izzie and George — wasn't quite born yet as Alex joined the central fray later, but the groundwork is laid for a family of doctors fans will follow for the next decade. 

2. "Sanctuary" and "Death and All His Friends" — Season 6, Episodes 23 and 24 
What happened: A shooter (Michael O'Neill) with a vendetta against doctors — specifically Derek, Lexie and Webber — rampages through the hospital, killing Reed and Percy, among countless others, while injuring Alex, Derek and Owen. Meredith also suffers a miscarriage when she believes Derek to be dead.
Why it was a game-changer: The first shock of Reed's execution-style death kept fans on the edge of their seat throughout the two hours, which also saw Owen finally choose Cristina over Teddy, Callie and Arizona get back together and Cristina find the confidence to save Derek's life. It also reminder Grey's fans that no one is safe in Shondaland.

1. "Now or Never" — Season 5, Episode 24
What happened: After Izzie wakes up from surgery, she's unable to remember anything. Eventually, she starts to remember after Alex screams at her, but then she flatlines. Elsewhere, the other doctors attempt to save a man who was hit by a bus. When the man writes 007 on Meredith's hand, they realize the patient is actually George, who earlier in the episode announced he was enlisting in the Army. As both Izzie and George flatline, we see a vision of the pair — Izzie in her pink prom dress and George in his Army uniform — in the elevator. Unfortunately, Army George doesn't get on the elevator, indicating that he dies in the final moments of the finale. Also, because of the craziness, Meredith and Derek get married on a post-it note.
Why it was a game-changer: Even though it was leaked that T.R. Knight was leaving the series, George's death was a shocking moment in which Rhimes masterfully threw Grey's fans for a loop with the 007 twist. The post-it note nuptials was also a source of contention with viewers until the pair finally made their marriage official two seasons later. 

What were your favorite Grey's Anatomy episodes? Are there any we're missing from this list? Hit the comments!

Grey's Anatomy returns this fall on ABC.