Most of her novels belong to one of two sequences, referred to as "Kairos" and "Chronos", from the two ancient Greek words for time. "Chronos" refers to chronological or sequential time, while "Kairos" signifies a time in between, a moment of indeterminate time in which something special happens. (Although both sequences contain speculative elements, the Chronos sequence is primarily realistic, while the Kairos sequence, which includes A Wrinkle in Time, is clearly sf/fantasy.)
- Time Quartet (concerning the Murry family)
- O'Keefe novels (concerning the children of Meg Murry)
- The Arm of the Starfish (1965)
- Dragons in the Waters (1976)
- A House Like a Lotus (1984)
- An Acceptable Time (1989)
- Austin family novels
- Meet the Austins (1960)
- The Moon by Night (1963)
- The Young Unicorns (1968)
- A Ring of Endless Light (1980)
- The Anti-Muffins (1980)
- The Twenty-four Days Before Christmas (1984)
- Troubling a Star (1994)
- A Full House: An Austin Family Christmas (1999)
- All Girls Want Bad Boys: And no boy is a clearer example than Zachary Gray, who appears in The Moon by Night, A Ring of Endless Light, A House Like a Lotus, and An Acceptable Time. His bad-boy appeal transcends series; he gets involved with both Vicky Austin and Polly O'Keefe.
- Buy Them Off: In The Young Unicorns, they learn at the end that the doctor who had done so much to help Emily after she had been blinded — had been the person to blind her. (Albeit accidentally.)
- Canon Welding: L'Engle first connected her "Kairos" and "Chronos" series when Canon Tallis from Kairos novel The Arm of the Starfish appears in Cronos novel The Young Unicorns; several characters from each series would cross over later.
- Character Overlap: The Kairos and Chronos sequences are connected by several supporting characters — including Canon Tallis and Zachary Gray — who appear in both, as well as in some of L'Engle's other works.
- Deadpan Snarker: She was once asked in an interview if the 2004 version of Wrinkle lived up to her expectations.Yes. I expected it to be bad, and it was.
- Dreaming of Times Gone By: At the end of A Heart Like a Lotus, Polly has a dream of going into the cave of Blessed Theola, a long-dead mystic. Polly, in the dream, understands that her vision of bubbles holding galaxies, and a loving hand holding the bubbles, was Theola's vision of divine love (in this case, it's more metaphorical truth than factual reality.)
- Dreaming the Truth: In The Other Side of the Sun, Stella (an Englishwoman) goes to live with her husband's father in the Deep South shortly after The American Civil War. After a dream involving fireflies and her husband metamorphizing into a (black) man she had met there, she wakes to the realization that her husband and this man are half-brothers.
- Dude Magnet: In her young adult novels, both Vicky and Polly qualify.
- Dude, She's a Lesbian: A non-romantic variant in A House Like a Lotus, where Polly's parents have to explain to her that Max, her mentor and friend, is in fact a lesbian, and it matters because people might start to think Polly is one, too.
- Friendly, Playful Dolphin: Vicky in A Ring of Endless Light helps out at an institute studying dolphins and trying to figure out how to communicate with them—bordering on Sapient Cetaceans. The dolphins aren't all sweetness and light though—one dolphin loses her calf and goes into spasms of grief, slamming herself against the walls of her pool.
- Giver of Lame Names: Canon Tallis, who is given the honor of naming Meg and Calvin O'Keefe's first child. He comes up with Polyhymnia. It's a lovely name with a lovely meaning (referring to holy music), but it's laughably inappropriate for 1960's America, and no one knows how to spell or pronounce it. The girl goes by "Polly" in later life. (Meg and Calvin never let him name another kid.)
- Glad-to-Be-Alive Sex: Subverted in A Ring of Endless Light. Vicky and Leo discuss how being close to death has made them more interested in expressing life. Leo uses this as a come-on (including mentioning that his parents had sex as part of their mourning process), but Vicky isn't interested.Vicky: Why have I been so hungry?
Leo: Because eating is part of life. So is loving.
Vicky: Let's concentrate on eating, then.
- Happy Ending Override: Troubling a Star brings back the fictional country of Vespugia from A Swiftly Tilting Planet and reveals that the events of the latter book only delayed the country's dictatorial government from coming to power by about 10 or 15 years, rather than averting it entirely.
- Mama's Baby, Papa's Maybe: In The Love Letters, Charlotte fled to Portugal because when she told her husband she was pregnant, he had asked her who the father was. (It was him.)
- Orgasmatron: The Young Unicorns has a young-adult-friendly version of the trope: a Micro-Ray that can directly stimulate the pleasure center of the brain. The experience is described as feeling like flying.
- Questionable Consent: In A House Like a Lotus. Renny, a medical student who is several years older than Polly, has sex with her when she is in shock over a traumatic event and in his care. Polly, the narrator, doesn't act like Renny did anything wrong, but to modern eyes, he definitely did.
- Sliding Scale of Idealism vs. Cynicism: L'Engle was very interested in the question, and though she believed in a divine Providence, she didn't shy away from characters who are justifiably cynical. A Ring of Endless Light is a good example, where Suzy has firmly decided that Humans Are Bastards, but Vicky spends the book on a search for meaning in a world with so much pain.
- Taking the Veil: In A Severed Wasp, a minor character has this as her backstory — after her divorce.