Call it a “role” all you want. For any actor who got his or her start after 1990, a guest spot on Law & Order is more like a rite of passage.

While well-known actors such as Robin Williams, Frank Langella, Henry Winkler, Angela Lansbury, Jerry Lewis, Ellen Burstyn, Carol Burnett, and even Julia Roberts have filled in as special guest stars over the years, here are 28 actors who appeared on the show before they were stars (dun dun).

1. PHILIP SEYMOUR HOFFMAN: SEASON 1, EPISODE 14

Fifteen years before he was clearing space on his bookshelf for a Best Actor Oscar, the late Philip Seymour Hoffman made his on-screen debut in Law & Order’s first season. (The 1991 episode, “The Violence of Summer,” is also notable for being one of the few in which “Order” comes before the “Law.”)

2. JENNIFER GARNER: SEASON 6, EPISODE 23

Less than a year into her career, Jennifer Garner played temptress to Benjamin Bratt’s happily married Detective Curtis in the show’s sixth season finale, which was notable for its lack of the show’s typical “first comes law, then comes order” format. Instead, it follows the series’ key players in the aftermath of witnessing an execution at Attica.

3. CLAIRE DANES: SEASON 3, EPISODE 1

Claire Danes was clearly tinkering with her now-famous “cry face” at the tender age of 13, when she played the distraught daughter of a sometime-prostitute and murder suspect with her own romantic links to the murder victim. Six Feet Under star Lauren Ambrose makes one of her earliest career appearances in the same episode.

4. TY BURRELL: SEASON 11, EPISODE 2

Modern Family’s father of the year Ty Burrell was a bit of a latecomer to the game; he was 33 years old when he was cast in his first on-screen role in the 2000 episode “Turnstile Justice,” in which a mentally unstable homeless man is accused of killing a woman on the subway. The producers must have liked what they saw, because they brought Burrell back two seasons later to play a Marine marksman-turned-kidnapper.

5. ROONEY MARA: SEASON 7, EPISODE 20 (SVU)

By now, most people know that a year after (barely) appearing in the straight-to-video Urban Legends: Bloody Mary, Oscar-nominated actress Rooney Mara appeared in an episode of Law & Order: Special Victims Unit as a formerly overweight teen who bullies overweight teens. Why do most people know this? Because she caused a bit of a PR stir when she was quoted in Allure as saying the experience “was so awful.” Fans of the series were none too happy with Mara’s criticism, but she was quick to respond, clarifying that, “If anything, I didn't mean that the storyline was ridiculous; I meant that humanity is ridiculous.”

6. KATE MARA: SEASON 8, EPISODE 8

Rooney isn’t the only Mara to count L&O among her earliest roles. It’s also the show (albeit the original edition) that gave big sister Kate her first paying gig in 1997 as Jenna Erlich, the daughter of a murdered bail bondsman.

7. JOHN KRASINSKI: SEASON 3, EPISODE 11 (CRIMINAL INTENT)

A year before he began giving sideways glances to the documentary crew of The Office for nine seasons, John Krasinski was the anti-Jim Halpert when he played a violent—and possibly homicidal—high school basketball player facing off against Vincent D’Onofrio in a 2004 Law & Order: Criminal Intent.

8. JESSICA CHASTAIN: SEASON 1, EPISODES 2, 3 and 13 (TRIAL BY JURY)

In the span of less than a year beginning in the fall of 2011, now-two-time Oscar nominee Jessica Chastain went from being in no movies to being in, well, just about every movie. One of the shows that got her there, after guest spots on ER and Veronica Mars, was the single-season snoozer of a Law & Order spinoff, Trial By Jury, on which she played an assistant district attorney.

9. PETER FACINELLI: SEASON 5, EPISODE 14

Three years before his breakthrough role as teenaged stud (but 25 at the time) Mike Dexter in Can’t Hardly Wait, Peter Facinelli was playing another teenaged stud, this one at the center of a points-for-sex rape scandal, in his second credited performance.

10. VERA FARMIGA: SEASON 8, EPISODE 12

After a recurring role on the short-lived series Roar, starring Heath Ledger, Oscar nominee Vera Farmiga did the L&O thing in 1998 as the daughter of a convicted murderer who goes on her own mini killing spree.

11. EDIE FALCO: SEASON 3, EPISODE 15

By the time she made her first of four appearances on L&O—all of them as attorney Sally Bell—Edie Falco was already becoming an increasingly familiar face to fans of American independent cinema, having appeared in Hal Hartley’s The Unbelievable Truth and Trust and Nick Gomez’s Laws of Gravity. But her introduction to television audiences came with L&O, and it is on the small screen that she would later find her greatest success with shows like The Sopranos and Nurse Jackie.

12. JULIANNA MARGULIES: SEASON 3, EPISODE 17

Before they were warring spouses on The Good Wife, Julianna Margulies—as a military lieutenant—played a brick wall to Chris Noth’s investigation into the death of a female Navy officer at a Manhattan hotel. The role was Margulies’ second ever; two years earlier she had played a prostitute in the Steven Seagal actioner Out for Justice.

13. ROB MCELHENNEY: SEASON 8, EPISODE 1

It’s Always Sunny in Philadelphia star Rob McElhenney wasn’t even old enough to drink at Paddy’s Pub when he appeared as one half of a thrill-killing duo who turns witness for the state. The role is actually referenced in the original Sunny pilot, when a gorgeous transsexual (played by Homeland’s Morena Baccharin) tells McElhenney how much she liked him in the show.

14. EMMY ROSSUM: SEASON 8, EPISODE 10

Shameless star Emmy Rossum was just 11 years old when she landed her first on-screen appearance in 1997. So we’re guessing/hoping that much of the episode’s plot—which involved an Egyptian family’s fight over whether or not the pre-teen should be circumcised—was a bit over her head.

15. LEIGHTON MEESTER: SEASON 9, EPISODE 15

As a teenager living in a shelter who may know more than she’s letting on about the circumstances surrounding the death of a classmate, Leighton Meester’s first role is a far cry from Gossip Girl’s Blair Waldorf in the glamour department. But her ability to sass all those around her, including Detectives Briscoe and Curtis, is evident.

16. CLARK GREGG: SEASON 1, EPISODE 12

Three years after making his big-screen debut in the role of “Stage Manager” in David Mamet’s Things Change, soon-to-be Agent of S.H.I.E.L.D. Clark Gregg got mixed up in an investigation into the bombing of an abortion clinic in the first season of L&O.

17. CAMRYN MANHEIM: SEASON 1, EPISODE 12

Camryn Manheim made her television debut in the first season of L&O, in the same episode as Gregg. She would go on to star in two more episodes over the next three years.

18. AMANDA PEET: SEASON 6, EPISODE 5

Amanda Peet channeled her inner Patty Hearst for a 1995 L&O episode in which she claimed that she was kidnapped and forced to partake in a recent crime spree that has resulted in the death of four individuals.

19. PETER SARSGAARD: SEASON 6, EPISODE 6

Less than two months before he made his film debut in Dead Man Walking, Golden Globe nominee Peter Sarsgaard was just another college student caught up in the middle of a murder/cyber-stalking investigation.

20. ALLISON JANNEY: SEASON 2, EPISODE 12

With nearly 100 credits on her resume, Allison Janney is one of those actresses who seems to have been around forever. But one of her earliest roles was in a small part in a 1992 episode of L&O that follows the murder of a soap star. Two years later she appeared in a second episode of the series, this time playing a witness against the Russian mob.

21. GIL BELLOWS: SEASON 1, EPISODE 14

While his official acting debut came in a little-seen 1988 film called The First Season, Gil Bellows’ second professional credit—and first television gig—was as Hoffman’s scene partner-in-crime. Three years later, Bellows would share screen time with Tim Robbins and Morgan Freeman in his breakthrough role in The Shawshank Redemption. In 1997 he returned to the small screen in a big way as the (sometime) romantic lead in Ally McBeal.

Fun fact: Samuel L. Jackson was also one of this same episode’s guest stars; though he was far from a household name at the time, he had made an impression with small but memorable parts in Do the Right Thing, Coming to America, and Goodfellas.

22. ELLEN POMPEO: SEASON 6, EPISODE 16

Grey’s Anatomy star Ellen Pompeo played the lone survivor of an attack that took the lives of her mom and brother, and landed her father in jail. But as her dad’s trial progresses, fingers start pointing in her direction. Four years later, Pompeo played a similar role in a different episode of L&O, but this time the crime was sororicide.

23. CHANDRA WILSON: SEASON 2, EPISODE 18

Four years before Pompeo’s L&O debut, her future Grey’s Anatomy co-star Chandra Wilson made her first of three L&O appearances (the latter two for SVU) in the (appropriately) hospital-themed “Cradle to the Grave,” in which a baby is found frozen to death in an emergency room.

24. MICHAEL PITT: SEASON 8, EPISODE 17

Michael Pitt has never conformed to the typical “rising young star” formula, not even when he was just starting out at the age of 17 and starred in “Carrier,” a 1998 L&O episode that played a bit like the movie Kids; it told the story of an HIV positive young man who is knowingly infecting others with the disease.

25. SARAH PAULSON: SEASON 5, EPISODE 4

Sixteen years before she was well-known enough to score a big promo as a “special guest star” on SVU, Sarah Paulson was stirring up a whole lot of family drama in her first-ever role in the original series’ fifth season, as the daughter of a murder victim who also may or may not be sleeping with her stepfather.

26. CHRIS MESSINA: SEASON 6, EPISODE 2

Being killed in a 1995 episode of Law & Order wasn’t exactly the breakthrough role Chris Messina—star of The Mindy Project and The Newsroom—needed. But it didn’t prevent him from appearing on the show on two more occasions in the next eight years (in different roles, obviously).

27. PAUL WESLEY: SEASON 2, EPISODE 1 (SVU)

In the same year that he landed a recurring role on Guiding Light, The Vampire Diaries star Paul Wesley—then just 18 years old, and going by the name Paul Wasilewski—made his Law & Order debut as an uncooperative head of security.

28. SARAH WAYNE CALLIES: SEASON 4, EPISODE 17 (SVU)

The Walking Dead’s Sarah Wayne Callies has kept herself busy with television gigs for the past decade, but it all started with a 2003 episode of SVU. She plays a one-percenting wife who used to be a prostitute, whose testimony could provide invaluable to Detectives Benson and Stabler in a rape and murder case.

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Images courtesy of NBC Universal Television.