1 of 10
Hazel Lancaster and Augustus Waters, The Fault in Our Stars
First Encounter: Wry sixteen-year-old Hazel meets Augustus, a hot, sarcastic 17-year-old with a crooked smile, at their cancer support group. ''Goddamn,'' Augustus said quietly. ''Aren't you something else?''
Defining Moment: He reads her favorite book An Imperial Affliction.
Relationship Challenges: Hazel's diagnosis is terminal.
Why They Work: Because they both understand what it feels like to be young and sick and still fully, hilariously, passionately alive. Because of Amsterdam. Because they deserved three lifetimes together. —Karen Valby
2 of 10
Bella and Edward, The Twilight Saga
First Encounter: Bella walked into science class. Her scent ignites Edward's thirst for human blood — and he can't get away from her fast enough.
Defining Moment: In the parking lot outside Forks High, Bella walks to her car and is nearly crushed by an out-of-control-van. Edward's vampiric-reflexes save her. The rest goes down in Twilight history.
Relationship Challenges: What doesn't challenge their relationship? For starters, dozens (maybe hundreds) of vampires who want Bella dead for different reasons, Edward's refusal to make her immortal, Bella's feelings for her werewolf bestie Jacob, and their miracle baby — a half-vampire-half-human-fetus who nearly kills Bella.
Why They Work: Bella and Edward's relationship captures the moody, electric, and all-consuming passion of a first love — and they get to experience it for eternity. —Denise Warner
3 of 10
Katniss and Peeta, The Hunger Games trilogy
First Encounter: It began with a loaf of bread and an act of kindness.... Though Peeta, a baker's son, made his first lasting impression on Katniss when he threw her a loaf of burnt bread that allowed her hungry family to eat, the two don't really get to know each other until they are sent to compete in the nationally televised fight-or-die reality show/sacrifice ritual, The Hunger Games.
Defining Moment: With Peeta injured, ill, and on the verge of death, Katniss kisses Peeta knowing cameras will capture their courtship and sponsors will send them food and medical supplies. It's her version of returning the favor.
Relationship Challenges: Because of her hard-scrabble background Katniss almost unwaveringly looks out for herself, so there's little room for anyone else in her heart or mind — though a certain rugged hunting partner named Gale does confuse her feelings. Later in the series, a drastic shift in Peeta's personality (after he's tortured with tracker jacker venom) complicates the showmancers' yin-yang dynamic further.
Why They Work: Peeta is a fundamentally good-hearted, smooth-talking person with sensitivity that balances out Katniss's edge, self-consciousness, and lack of social propriety. He truly loves her, which she needs and appreciates — even if it takes her a little while to realize it. —Lanford Beard
4 of 10
Tris and Four, Divergent
First Encounter: After Tris jumps off the top of a train into a net many feet below, Four is the blue-eyed leader who helps her up.
Defining Moment: Tris and Four have a heart-to-heart atop an abandoned Ferris wheel.
Relationship Challenges: Four trains Tris in the first book, making their relationship forbidden. More importantly, Tris fears intimacy.
Why They Work: Despite her tightly wound, fiercely independent nature, Tris is uncontrollably drawn to Four. He supports and protects her without turning her into a damsel in distress. They're very much equals. —Stephan Lee
5 of 10
Rose and Dimitri, Vampire Academy
First Encounter: After two years on the run from vampire society, Rose and her best friend Lissa are finally caught by the legendary guardian Dimitri in all his six-foot-seven, duster-sporting glory.
Defining Moment: Though Rose initially dismisses Dimitri's romance cover looks as ''irrelevant,'' she quickly revises this opinion during their hot and sweaty training sessions. But the real turning point comes when Dimitri walks in on her getting physical with the royal Moroi Jesse Zeklos. Let's just say D's ensuing jealousy isn't what one would call mentorly.
Relationship Challenges: At seven years her senior, Dimitri feels he's too old for Rose. Oh, and then there's his whole ''becoming a murderous, bloodsucking fiend'' phase. That'll put a damper on any relationship.
Why They Work: Longing gazes and sexually loaded fight scenes aside, nothing says true love quite like following your beau to Siberia to enact your final promise to him — even (or perhaps especially) if that final promise is to kill him. —Tara Fowler
6 of 10
Lena and Alex, Delirium
First Encounter: Lena spots Alex causing mischief on the day of her evaluation, a test that will determine with whom she'll be paired for the rest of her life. She re-meets him a few days later, when Alex catches Lena and her best friend Hana trying to break into the evaluation center.
Defining Moment: Lena tracks Hana to an illegal party that's eventually broken up by the police. Terrified, she seeks refuge from the raid with Alex — and there, the couple kiss for the first time.
Relationship Challenges: Well, they live in a totalitarian society that vilifies the very idea of love, so PDA (any DA, really) is completely out of the question. And given the ending of the first book, the likelihood of Lena and Alex ending up together seems slim to none.
Why They Work: Daring Alex teaches cautious Lena to question her oppressive society, helping her to become a kickass, Katniss-esque freedom fighter. Also, both of them are really, really attractive. —Hillary Busis
7 of 10
Katherine and Michael, Forever...
First Encounter: They meet at a New Year's Eve party — a suitably low-key beginning for one of young adult fiction's most realistic, relatable relationships.
Defining Moment: The first time Katherine and Michael are alone together, he turns to her and says, ''Can I kiss you?'' Coupledom was simple as that in 1975.
Relationship Challenges: After high school graduation, the two separate for the summer, and Katherine finds herself attracted to a fellow camp counselor. How can young love survive?
Why They Work: The secret to this sweet, ultimately mundane romance lies in this statement from author Judy Blume: ''My daughter Randy asked for a story about two nice kids who have sex without either of them having to die.'' —Hillary Busis
8 of 10
Jessica and Marcus, the Jessica Darling books
First Encounter: They've known each other for years, but their relationship is really catalyzed when Marcus asks Jessica to pee in a cup for him so that he can pass a drug test. True romance!
Defining Moment: Alone in a car after weeks of marathon phone conversations, Marcus pulls Jessica close and...bites her lip. She has no idea if it counts as their first kiss.
Relationship Challenges: Marcus is unpredictable, inscrutable, and fond of mind games, which makes it impossible for Jessica to ever really understand his motives. He was also best friends with Heath, Jessica's best friend's brother, who dies of a drug overdose before the first book begins — and Jessica partially blames him for Heath's death.
Why They Work: Jessica and Marcus are intellectual equals who share a love of crappy pop culture, witty comebacks, and subverting the dominant paradigm — in other words, the poster couple for teenage smartasses everywhere. —Hillary Busis
9 of 10
Ethan and Lena, Beautiful Creatures
First Encounter: Lena, the new girl in school, turns up in Ethan's English class — though he soon realizes that he's been having dreams about her for weeks. A few days later, he almost hits her with his car. Naturally, sparks fly.
Defining Moment: Ethan has dinner with Lena's crazy family — half of whom are good witches (or ''Casters''), half wicked witches. There's a fight, and Ethan ends up fainting...perhaps because Lena has just called him her boyfriend for the first time.
Relationship Challenges: When Lena turns 16, she may or may not become an evil sorceress, which is sort of a buzzkill. Also, Casters can't physically consummate relationships with mortals without killing them.
Why They Work: Initially, Lena and Ethan bond over their shared nature as outsiders; she doesn't belong in static Gatlin, S.C., and he yearns to leave the town for bigger and better things. Eventually, they learn that they're essentially the reincarnations of a pair of doomed lovers from the Civil War era — which makes their pairing nothing short of destiny. —Hillary Busis
10 of 10
Jace and Clary, The Mortal Instruments
First Encounter: Clary stumbles upon Jace at NYC nightclub Pandemonium while he and his fellow Shadowhunters attack a demon. Clary's introduction to the Shadowhunting world is only a peek at Jace's enigmatic character.
Defining Moment: The two have a classic will-they/won't-they relationship, each finding the other slightly annoying in the beginning, but they finally share a swoon-worthy kiss in the Institute's Greenhouse in the first book, City of Bones.
Relationship Challenges: At the end of City of Bones, Clary and Jace discover they share the same parents, Valentine Morgenstern. (Yeah, we were grossed out too.) Incest ranks pretty high on the list of relationship complications, and they have to make the switch from couple to siblings. Additionally, Clary's best friend, Simon, has feelings for her completing yet another quintessential YA love-triangle.
Why They Work: Eventually Clary and Jace learn they are not, in fact, related. Whew! With that barrier out of the way, they can continue on with their passionate, near-obsession with each other. Things are never easy for them (see: City of Fallen Angels where Jace is controlled by the demon Lilith and dreams of killing Clary) but nothing is ever easy for the Shadowhunters. —Breia Brissey