
After their parents died, Henry, Jessie, Violet, and Benny Alden ran away to live by themselves in an old boxcar that they found in the woods. Although they were aware that they had a living grandfather who should be their legal guardian, they were afraid to go and live with him because their parents had (apparently) told them that he was mean. The source of the quarrel between the children’s parents and grandfather is never completely revealed, but it seems that he had disapproved of the children’s mother, so the children assumed that he would similarly dislike them.
However, after the children’s worried grandfather eventually locates them, they learn that he is actually a nice person who really cares about them. He is a wealthy man, and they go to live in his mansion. As a special surprise for the children, he even brings their old boxcar to his property so they can continue to use it as a playhouse. For the rest of the series, the children solve mysteries in various settings. They are very self-sufficient and do their investigating with little or no adult help. The children are generally hard-workers, something that their grandfather takes pride in and encourages.

There are several aspects of the children’s past that are never completely explained. For instance, we don’t know exactly how the children’s parents die in the original stories (except for the father’s death, which is explained in the early 1924 edition of the first book – his death, darkly, was alcohol-related, which is probably why this part was removed from the reissue of the story in the 1940s – the mother was already dead before the book began) or what they had told the children about their grandfather. Patricia MacLachlan wrote a prequel to the series called The Boxcar Children Beginnings to explain the children’s lives before the series began, and one of the later additions to the series, #149 The Day of the Dead Mystery, briefly mentions the children’s parents dying in a car accident, which was the premise of The Boxcar Children Beginnings.
In a way, the series always felt a little odd to me for not saying much about the circumstances of the parents’ deaths. The Alden children are always portrayed as being very self-sufficient, looking after themselves and each other, and they never seem terribly sad about their parents and only rarely talk about missing their parents at all. Even in the first book, little Benny doesn’t cry or talk about wanting his parents or missing them. I guess the author mostly wanted to get on with the adventure, but I would expect that real children would have more grief to get through.
The first books in the series were written by Gertrude Chandler Warner, but the series continued far after her death with new books written by other authors. Because they were written and published through different decades, the art style in the books varies over time. All or most of the books contain pictures inside as well as cover art. Some of the pictures are very simple sketches, while others are more detailed and lifelike. The later books in the series tend to have more detailed drawings than the earlier ones. The first book in the series has iconic silhouette style pictures, though.
In the early books, the ones written by Gertrude Chandler Warner, the children aged in the stories. As the kids aged, their ages weren’t always specified in each book, but Henry grew old enough to attend college. However, as the series was continued, their ages reset to the ages they were in the first book and became frozen with Henry as age 14, Jessie as age 12, Violet as age 10, and Benny as age 6.
I haven’t finished entering in all of the books in this series to date, partly because there are so many and partly because the series is still being written. There may be more updates here later.
Books in the Series by Gertrude Chandler Warner:

#1 The Boxcar Children (1924, 1942)
The first book explains how the children ran away and lived in a boxcar and how their grandfather discovered where they were and took them in. There are two versions of this story, the shorter one that most of us know from childhood, and the longer version that was originally written in the 1920s.
#2 Surprise Island (1948)
The children spend the summer on an island, finding old relics in a cave and learning the identity of a man who had amnesia.

#3 The Yellow House Mystery (1953)
The Aldens investigate a mysterious disappearance many years ago.
#4 Mystery Ranch (1958)
The Alden children visit their grandfather’s sister on the ranch where the two of them grew up and discover why people are pressuring her to sell the ranch to them.
#5 Mike’s Mystery (1960)

#6 Blue Bay Mystery (1961)
The Alden children camp out on a supposedly deserted island with their grandfather and a couple of friends, but they find out that they’re not as alone as they think they are.
#7 The Woodshed Mystery (1962)
The farm where Grandfather Alden grew up still holds a secret from the American Revolution.

#8 The Lighthouse Mystery (1962)
The Boxcar Children and their Grandfather rent a lighthouse for vacation, but someone is conducting a strange experiment in a nearby house.
#9 Mountain Top Mystery (1964)
The Aldens are stranded on a mountain due to landslide and uncover a secret involving a Native American woman.

#10 Schoolhouse Mystery (1965)
The Boxcar Children deal with a conman cheating people out of valuable antiques.
#11 Caboose Mystery (1966)
Grandfather Alden arranges for the kids to travel by train in a caboose, and they find a mystery involving a missing diamond necklace.

#12 Houseboat Mystery (1967)
The Aldens are traveling on a houseboat, but someone is watching them, and they seem to want something on the boat.
#13 Snowbound Mystery (1968)
The Alden children are staying at a cabin the woods when they are snowed in with a secret message and a family that is looking for something.
#14 Tree House Mystery (1969)
The Boxcar Children are building a tree house with the kids next door when they realize that the house next door has a window that they never noticed before.

#15 Bicycle Mystery (1970)
The Boxcar Children are taking a cross-country bicycle trip to visit their Aunt Jane when a lost dog leads them into another mystery.
#16 Mystery in the Sand (1971)
The kids are spending their vacation at the beach when they find a locket in the sand.

#17 Mystery Behind the Wall (1973)
The Boxcar Children and a new friend discover an old treasure hunt created by a girl who used to live in their house, which leads to a valuable coin collection.
#18 Bus Station Mystery (1974)
#19 Benny Uncovers a Mystery (1976)
Books By Other Authors:

#20 The Haunted Cabin Mystery (1991)
#21 The Deserted Library Mystery (1991)
The Boxcar Children are helping to clean up an old library so it can get landmark status, but someone wants something inside the library.
#22 The Animal Shelter Mystery (1991)
#23 The Old Motel Mystery (1991)
#24 The Mystery of the Hidden Painting (1992)

#25 The Amusement Park Mystery (1992)
Someone is stealing antique carousel horses and substituting them with fakes!
#26 The Mystery of the Mixed-Up Zoo (1992)
Grandfather Alden’s friend owns a a zoo, and some strange things have been happening there that put the animals in danger.

#27 The Camp-Out Mystery (1992)
Strange things happen on a camping trip, and the Aldens wonder who could be trying to drive them away from the camp grounds.
#28 The Mystery Girl (1992)
The Boxcar Children take temporary jobs working in an old-fashioned general store, but they start to worry about the other girl who works there because she seems like she’s hiding something or from someone.
#29 The Mystery Cruise (1992)
Someone is sabotaging a cruise to prevent someone from reaching their destination on time to receive an inheritance.

#30 The Disappearing Friend Mystery (1992)
#31 The Mystery of the Singing Ghost (1992)
#32 Mystery in the Snow (1992)
The Boxcar Children are participating in a series of winter games at a ski lodge, but someone is trying to sabotage the competition.
#33 The Pizza Mystery (1993)

#34 The Mystery Horse (1993)
#35 The Mystery at the Dog Show (1993)
#36 The Castle Mystery (1993)
The Boxcar Children look for a stolen Stradivarius violin in a castle that’s being turned into a museum.
#37 The Mystery of the Lost Village (1993)

The Boxcar Children try to find signs of a lost village near a Navajo reservation to save the land from being developed.
#38 The Mystery of the Purple Pool (1994)
The Boxcar Children visit New York City with their grandfather, but strange things are happening at their hotel.
#39 The Ghost Ship Mystery (1994)

The Boxcar Children help to resolve a historical mystery and ghost story, discovering the truth behind the sinking of a ship years before.
#40 The Canoe Trip Mystery
#41 The Mystery of the Hidden Beach
#42 The Mystery of the Missing Cat

#43 The Mystery on Stage (1994)
Someone is trying to sabotage a play of The Wizard of Oz!
#44 The Dinosaur Mystery (1995)
The Alden children are volunteering at a museum, helping to prepare for a new dinosaur exhibit, but someone is sabotaging their efforts!
#45 The Mystery of the Stolen Music (1995)

#46 The Chocolate Sundae Mystery (1995)
#47 The Mystery of the Hot Air Balloon (1995)
#48 The Mystery Bookstore (1995)
#49 The Mystery of the Stolen Boxcar (1995)
#50 Mystery in the Cave (1996)
The Boxcar Children are at a park with caves to explore, but they keep meeting suspicious people with hidden motives, who don’t seem to want them in the caves.
#51 The Mystery on the Train (1996)
A collection of valuable movie posters is stolen from a girl traveling on the same train as the Boxcar Children
#52 The Mystery of the Lost Mine (1996)
#53 The Guide Dog Mystery (1996)
#54 The Hurricane Mystery (1996)
#55 The Mystery of the Secret Message (1996)
#56 The Firehouse Mystery (1997)
#57 The Mystery in San Francisco (1997)
#58 The Mystery at the Alamo (1997)
The Boxcar Children are visiting San Antonio, Texas, when they are invited to be extras in a movie about the Alamo. But, someone tries to sabotage the project and steal an heirloom ring!
#59 The Outer Space Mystery (1997)
#60 The Soccer Mystery (1997)
The Boxcar Children sign up for a summer soccer league, but someone starts sabotaging their team.
#61 The Growling Bear Mystery (1997)
#62 The Mystery of the Lake Monster (1998)

#63 The Mystery at Peacock Hall (1998)
The Boxcar Children search for a hidden treasure in a relative’s house.
#64 The Black Pearl Mystery (1998)
#65 The Cereal Box Mystery (1998)
#66 The Panther Mystery (1998)
#67 The Mystery of the Stolen Sword (1998)
#68 The Basketball Mystery (1999)
#69 The Movie Star Mystery (1999)
#70 The Mystery of the Pirate’s Map (1999)
#71 The Ghost Town Mystery (1999)
#72 The Mystery in the Mall (1999)
#73 The Gymnastics Mystery (1999)
#74 The Poison Frog Mystery (2000)

#75 The Mystery of the Empty Safe (2000)
#76 The Great Bicycle Race Mystery (2000)
#77 The Mystery of the Wild Ponies (2000)
#78 The Mystery in the Computer Game (2000)
The Boxcar Children become play testers for a computer game, but someone is playing a more serious game, using puzzles to give them clues to a crime.

#79 The Mystery at the Crooked House (2000)
The Boxcar Children help Mrs. MacGregor solve an old riddle and learn the secrets of a mysterious woman who visited her family years ago
#80 The Hockey Mystery (2001)
#81 The Mystery of the Midnight Dog (2001)
#82 The Summer Camp Mystery (2001)

The Aldens join a summer camp where some of the other campers are trying to make them look bad.
#83 The Copycat Mystery (2001)
The Boxcar Children help at a Victorian farmhouse that’s been turned into a museum and encounter a bizarre practical joker.
#84 The Haunted Clock Tower Mystery (2001)
The Boxcar Children attend Grandfather Alden’s college reunion and find themselves in search of a treasure from the Civil War!
#85 The Disappearing Staircase Mystery (2001)
#86 The Mystery on Blizzard Mountain (2002)
#87 The Mystery of the Spider’s Clue (2002)

#88 The Mystery of the Mummy’s Curse (2002)
The Boxcar Children are helping to set up an exhibit at a museum when they realize that someone is stealing Egyptian artifacts!
#89 The Mystery of the Star Ruby (2002)
#90 The Stuffed Bear Mystery (2002)
#91 The Mystery at Skeleton Point (2002)

The Boxcar Children investigate the thefts of statues around a spooky house filled with skeletons.
#92 The Tattletale Mystery (2003)
A series of mysterious messages hint at a mystery involving the work of a deceased artist.
#93 The Comic Book Mystery (2003)
The Boxcar Children track down someone who is making fake copies of a rare comic book.
#94 The Ice Cream Mystery (2003)
#95 The Midnight Mystery (2003)
The Boxcar Children search for an inventor’s lost notebook in a house with her inventions and riddles
#96 The Mystery in the Fortune Cookie (2003)
#97 The Radio Mystery (2003)
The Boxcar Children perform a mystery radio play in a radio station that’s supposedly haunted.
#98 The Mystery of the Runaway Ghost (2004)
Is an old house haunted by the ghost of a runaway cow?
#99 The Finders Keepers Mystery (2004)
A set of old quilts in the attic of an old house hold the secret to a family mystery and a hidden treasure.
#100 The Mystery of the Haunted Boxcar (2004)

#101 The Clue in the Corn Maze (2004)
Someone is sabotaging a farmer’s corn maze and the farmer’s corn festival.
#102 The Ghost of the Chattering Bones (2005)
The Boxcar Children investigate a haunted bridge and search for a long-lost brooch.
#103 The Sword of the Silver Knight (2005)
An antique sword is stolen from a medieval fair.
#104 The Game Store Mystery (2005)
#105 The Mystery of the Orphan Train (2005)
The Boxcar Children are staying an a bed and breakfast in Kansas, where they learn the secrets of a pair of orphans from the past and the loss of a necklace.

#106 The Vanishing Passenger (2006)
The Boxcar Children search for a missing author, who vanished mysteriously on a train.
#107 The Giant Yo Yo Mystery (2006)
#108 The Creature in Ogopogo Lake (2006)
#109 The Rock and Roll Mystery (2006)
#110 The Secret of the Mask (2007)

#111 The Seattle Puzzle (2007)
#112 The Ghost in the First Row (2007)
The Boxcar Children investigate a series of strange things happening in an old theater.
#113 The Box that Watch Found (2007)
#114 A Horse Named Dragon (2008)
#115 The Great Detective Race (2008)
#116 The Ghost at the Drive-In Movie (2008)
Someone is sabotaging a drive-in movie theater, and a mysterious ghost appears!

#117 The Mystery of the Traveling Tomatoes (2008)
#118 The Spy Game (2009)
The Boxcar Children solve riddles to find a hidden treasure, but this treasure hunt isn’t quite what it seems!
#119 The Dog-Gone Mystery (2009)
A dog disappears from a dog training class.

#120 The Vampire Mystery (2009)
The Boxcar children are house sitting for a local author known for his novel about a vampire when it seems like the vampire might be trying to sabotage the sale of his house.
#121 Superstar Watch (2009)
#122 The Spy in the Bleachers (2010)
#123 The Amazing Mystery Show (2010)

#124 The Pumpkin Head Mystery (2010)
It’s Halloween and someone is sabotaging a pumpkin patch that offers spooky hayrides!
#125 The Cupcake Caper (2010)
#126 The Clue in the Recycling Bin (2011)
#127 Monkey Trouble (2011)
#128 The Zombie Project (2011)

The Boxcar Children are staying at a lodge with hiking trails when they see a zombie who is apparently a local legend.
#129 The Great Turkey Heist (2011)
The Boxcar Children help to set up a food bank around Thanksgiving, but someone is trying to sabotage it!
#130 The Garden Thief (2012)
#131 The Boardwalk Mystery (2013)
#132 The Mystery of the Fallen Treasure (2013)

#133 The Return of the Graveyard Ghost (2013)
A ghost is said to haunt the cemetery in Greenfield, demanding that people leave gifts at Halloween to avoid getting bad luck.
#134 The Mystery of the Stolen Snowboard (2014)
#135 The Mystery of the Wild West Bandit (2014)
#136 The Mystery of the Soccer Snitch (2014)
#137 The Mystery of the Grinning Gargoyle (2014)
#138 The Mystery of the Missing Pop Idol (2015)
#139 The Mystery of the Stolen Dinosaur Bones (2015)
#140 The Mystery at the Calgary Stampede (2015)

#141 The Sleepy Hollow Mystery
The Boxcar Children visit Sleepy Hollow at Halloween and have some frightening encounters with a headless horseman!
#142 The Legend of the Irish Castle (2016)
#143 The Celebrity Cat Caper (2016)
#144 Hidden in the Haunted School
#145 The Election Day Dilemma

#146 The Doughnut Whodunit
#147 The Robot Ransom
#148 The Legend of the Howling Werewolf
#149 The Day of the Dead Mystery
#150 The Hundred-Year Mystery
#151 The Sea Turtle Mystery

#152 Secret on the Thirteenth Floor (2019)
Strange accidents are happening on the thirteenth floor of an old apartment building. Is it all bad luck?
#153 The Power Down Mystery
#154 Mystery at Camp Survival
#155 The Mystery of the Forgotten Family

#156 The Skeleton Key Mystery (2020)
Someone is trying to sabotage a spooky escape room around Halloween!
#157 Science Fair Sabotage
#158 The Great Greenfield Bake-Off
#159 The Beekeeper Mystery
#160 The Mystery in the Magic Shop
#161 The Raptor Rescue
Boxcar Children Specials

#1 The Mystery on the Ice
#2 The Mystery in Washington, D.C.
#3 The Mystery at Snowflake Inn (1995)
The Boxcar Children spend their winter holiday at an historic inn in Vermont, where strange things are happening!
Boxcar Children Great Adventures
#1 Journey on a Runaway Train
#2 The Clue in the Papyrus Scroll
#3 The Detour of the Elephants
#4 The Shackleton Sabotage
#5 The Khipu and the Final Key
Supplemental Books
These are books written by various authors to accompany the series.

The Boxcar Children Cookbook (1991)
A cookbook companion to the Boxcar Children mystery series for children. By Diane Blain.