On Thursday, Grey's Anatomy will celebrate a momentous milestone as the show airs its 200th episode. With that in mind, TVGuide.com decided to look back to the very beginning to find out how the cast of the ABC medical drama joined the show.

"I was offered the role of Meredith. I had done a movie for the studio called Moonlight Mile, so the studio was aware of me. Then... I met Bob Orci and Alex Kurtzman. ... We sat down and talked about me possibly doing an arc on Alias. That didn't happen. Bob and Alex wrote a show called Secret Service. I really wanted to do that and the studio really wanted me to do Grey's instead. I wanted to do the Secret Service pilot that didn't go, of course; me and my brilliant choices. I read Grey's and I went and met Shonda and I decided to come on and do this. It was just an invitation and I happily accepted."

"I remember coming in and all the producers were there. I remember Shonda looking at me, and I was convinced she didn't like me. I was like, 'I didn't get that.' Then, I immediately went from that to the audition for House. When I finished that audition, I got a call saying, 'They want you to read with the actress who's playing the lead role in this.' I remember asking Shonda what that was [about] and she said, 'I was figuring out how to put you in the show.' I met Ellen, and her Boston accent lit me up because I was from Maine. So, I immediately had a great connection with her."

"I... went in for Bailey. I actually had a pair of scrubs and had my hair in braids. I played Bailey completely differently than Chandra Wilson did. The character of Bailey didn't resonate with me. I asked what else was available, and the part of Cristina was not yet cast. It's great — it's an antagonist, you get a good sense of who she is, she's very ambitious. I thought it would be great to play. ... I remember meeting T.R. Knight in the audition room. I went there early because Shonda and Betsy and the director Peter Horton wanted me to be comfortable because they had never seen me do Cristina. I did this scene for them a couple times. I was at first nervous, but they were like, 'No worries, you're good. You'll audition for the studio later.' ... I don't know how many days later, they offered me the part. It was amazing. I auditioned for the right people. I just thought they were so smart because I wasn't thinking I was auditioning for them. I was just going to read the scenes a couple times for them feeling relaxed. But they saw what I was going to do with this character."

"They had shot the pilot a year before it aired. They felt they needed to tinker with it a little more. I had done a pilot for ABC, [Secret Service], that didn't get picked up. They liked what I did in that, and they brought me in to do a screen test with Ellen. I guess they felt they needed a jerk, so they brought in this jerk. It worked out."

"I had to go to ABC in New York and go on tape with casting there. I was completely wrong for this character, but for whatever reason, they had me come in. It was one of those, 'I have absolutely nothing to lose' kind of auditions. Then I got called to come out to L.A. to do my studio and network auditions. I did the audition and they told me I had to come back later that evening for the network. It was me and one other actress. The note that I was given was, 'Everything is really good, but the other actor really took command. She was really in charge. You should probably bring some more of that with you to the audition.' I went in and I did that, and then it was over. I was descending down the stairs as they were all talking to the other actors thinking, 'This was a free trip to L.A.' I think it was the next day when I got the role."

"I did a standard audition. I had just come off a show that had gone all of five episodes on NBC. It hadn't been long after that that I got this call to go audition. I thought it went OK — uneventful, nothing earthshattering. I received a callback to come back in, and I was the only one who was called in for Dr. Webber. I remember going to Disney and Shonda and Peter Horton were there. I had gotten a couple of notes from Shonda, and I actually did a monologue for the scene that opens in the pilot where he's standing in the operating room telling the interns that the majority of them won't make it. I did that monologue and they asked me to step out for a minute and they discussed. I came back in and Peter Horton said, 'Well, what are you doing for the next five years or so. Do you want to have this role?' I said, 'Oh my God yes!'"

"I was performing as the Lady of the Lake in Spamalot. I got a call that several networks had come out to see the show and ABC was one of them and they had expressed interest in working with me on a seven- episode arc for one of their shows. They didn't know which one, so they wanted me to pick. I had done a pilot for ABC before, so we had a relationship already and I was thrilled. They sent me a stack of all the shows currently on the air as well as all their new pilots that had gotten picked up. I watched them all, knowing very well Grey's Anatomy was my favorite show, and that was in the pile. I decided Grey's was the one I wanted to try for... and they said, 'Great! We're going to fly Shonda Rhimes out to see you in Spamalot.' The next morning, we had brunch together, and I suppose that would have been the callback. She could have canceled that appointment if it didn't go well the night before. But she didn't, thank God. She revealed to me that she was going to be writing a character for me opposite George, and I was thrilled because I was in love with the character George O'Malley. Next thing I knew, I was starting to shoot in February of 2006. I felt so lucky."

"I went off and did Journeyman and then there was the writers' strike. I was waiting around in Hollywood with a young family going, 'Maybe we should just go back to Britain.' I got a phone call from my agent saying Shonda Rhimes called about meeting me. I was actually in Romania doing a movie with Woody Harrelson and Ron Perlman and he said, 'They need to see you on the day you land.' And the day I landed, I had been away for three months [and] it was my son's birthday. So I said, 'I'm sorry. I can't meet her it's my son's birthday. I hope she can understand.' Supposedly Shonda tells the story that her and Betsy, when they heard that, said, 'What a great guy.' So, it kind of paid off. I went and saw them the next day, and we just started chatting. I didn't read for it. They told me about this new character that... was going to be Iraq vet who was dark and messed up. It was between me and one other actor. Then, sure enough, I got a phone call that Shonda... decided to give me the role. I did not know what this character was going to be. I had to take the role in blind faith. He was designed to be Cristina's new love interest. Sandra and I hadn't met at that point. The first day Sandra and I met, we did a scene together and she was so sweet. She said, 'Thank you! Thank you for being a good actor.' And then we just hit it off from that point."

"I auditioned for this show two weeks after I had my son Luke, and I was not interested in auditioning for anything because I was interested in being a mother. But my agent called me and said, 'I wouldn't call you for any other reason other than Grey's Anatomy, because I know that's your favorite show.' So two weeks after I had the baby, I... auditioned for Nurse Rose [eventually played by Lauren Stamile]. I knew Patrick because I had worked with him two years prior, so he and I got along real well. But they picked the other girl and I was like, 'Man!' About a year later, I went in for a part that hadn't been named yet, but she was this sexually promiscuous, adventurous part, and I didn't get the role again. That was Melissa George's part, Sadie. They kept saying they really love me and I was like, 'If they really love me, I would have a part in the show." A month later, I got a three-episode offer to play Arizona Robbins."

"I didn't audition for this. I had worked with Shonda on Private Practice, so I auditioned for her there. That was incredibly nerve-wracking because she's this genius, brilliant lady, and I'm like, 'I just want to know you. I hear you're awesome. Your shows are incredible.' She actually cast me as a guest star on that and then cast me in a pilot that she did that didn't get picked up. She wrote this role for me on Grey's, but it was meant to be just two episodes and gone. In fact, they called to ask me about a different role that really would've been gone after two episodes. I couldn't do it. It conflicted with something. Thank God. There was no way I would've stuck around. Here we are 200 episodes!"

"Shonda had a pilot called Gilded Lilys that I tested for, so I knew Shonda a few months before. When I went in [for Grey's], I actually almost missed the auditions because I was at Comic-Con for Tomb Raider. I heard that Shonda had wanted me to come in, but I couldn't make it. That Monday, they said they still hadn't found anybody. I went in, and my first scene was kind of flirty. My second scene was me just blabbering a lot of medical dialogue. I probably heard two days later that I got the role. At that point, they had told me they were going to write our stories just off our personalities, so I guess I come across as a garbage eater or something. [Laughs] They had decided after they cast me that I would be Karev's new love interest. It was interesting. I had never been cast that way before."

"I was on the East Coast, so I sent a tape to casting in Los Angeles. A few days later, I was elated to find out that I got the part."

"I had little to no information about the role — simply that it was for a 'medical professional.' However, it was an excellent opportunity to create something rich that aligned with what speaks to me. To be honest, even though I was familiar with [casting director] Linda Lowey's office because of Scandal, I was still nervous as hell about this Grey's situation. [I] flubbed lines and had shaky hands, but I knew I had the director, Rob Corn, in my corner. When I got a call a few days later saying I had ‘a pin in me,' I was unbearably ecstatic. What I remember most, though, is what happened after the audition: struggling to figure out the job. I stayed up until midnight the night before my fitting Googling info on scrub colors. 'If they put me in this color, at least I'll know what job I have!' It wasn't until I picked up the script... that I even knew Stephanie's name or that she was an intern! It was a wild beginning."

"I auditioned a couple of times for different roles. I was in the waiting room with Tina Majorino before one of them, and the air conditioning kept going on and vigorously shaking the ceiling. It scared the crap out of both of us so many times. The last time I went in, I was coming directly from another shoot with no time to change. I had on thick black eye liner, knotted hair and fake tattoos all over. I guess they liked my character choice!"