These are a majority of the differences between The Maze Runner novel and film. I have taken out some of the differences that would cause major spoilers.
In the book, Thomas immediately remembers his name upon arriving in the Glade. In the film, he doesn't remember it until later that night after hitting his head while sparring with Gally; Gally is also a little different in the film. He's not quite as mean, and he doesn't initially distrust Thomas. He doesn't start distrusting him until Thomas survives a night in the Maze, killing a Griever in the process, and then Teresa comes up with the news that there will be no more new arrivals or supplies.
In the book, Teresa and Thomas can communicate with each other telepathically. This ability is not seen or referenced in any of the films. This ability and the connection that come from it was an surprisingly large component in the novels. Part of why they were close in the books is because they were not only communicating while she was in a coma, but at other stages throughout the series as well, so the lack of this ability in the films make the relationship between Thomas and Teresa feel a bit rushed.
In the book, moments after arriving in the Glade, Teresa goes into a coma for several weeks and triggers The End. In the movie, she's comatose only for a few days.
One of the more significant changes from book to screen was the interactions with the Grievers once the End was triggered. In the book, when the doors to the Maze stay open at nightfall, the Grievers take one Glader at a time each day. In the movie, the Grievers fully attack the Glade and kill many Gladers.
In the book, Thomas spends an entire day in the Slammer for going out into the Maze. In the movie, he only spends a night and no food.
In the book, the Gladers use hand-drawn maps of the Maze to study it. In the movie, they build a large model of the entire Maze. This was one change I felt worked well for the screen. The maps would have been nice, but I do like the physical representation of the Maze.
In the book, the serum that is used on the Glader after being stung by a Griever already exists in the Glade long before Thomas arrived. In the movie, Teresa brings the serum when she is sent up to the Glade.
In the book, the Changing doesn't happen until after you have been given the serum. In the film, the Changing is triggered the moment you are stung. The serum simply stops you from dying.
In the book, the Gladers have been in the Glades for two years. In the movie, they've been there for three years.
In the book, Beetle Blades are used to spy on the Gladers and report back to the Creators. In the movie, the Beetle Blades don't exist but the Creators spy on them through surveillance cameras in the Maze. I really don't like this change. I loved reading about the Beetle Blades and Thomas' reaction to them. The Beetle Blades remind me of the Sentinels in the TV show The Gifted, so I would have loved to see that on screen.
In the book, the surviving Gladers who escaped are ushered into a bus and put into dorm rooms. In the movie, they are ushered into a helicopter outside in the scorching sun.
In the book, Gally had been stung by a Griever long before Thomas had arrived and recognizes him. In the movie, Gally gets stung at the end when he escapes.
In the book, 30 Gladers were sent up in the Box. In the movie, Alby was the first one to arrive in the Glade, and he stayed alone for a month until the next Glader was sent up.
In the book, Teresa arrives the day after Thomas did. In the movie, she arrives a few days after Thomas arrives.
In the book, the Gladers meet the Creators at the end before they are killed by the rescuers. In the movie, the Creators are already dead when the Gladers escape the Maze.
In the book, Alby sacrifices himself so the Gladers can escape the Maze. In the movie, he dies before the Gladers plan their escape.
In the book, Gladers were able to figure out the clues through the map by recreating them through a wax paper and putting them on top of the other and they formed words (FLOAT, CATCH, BLEED, DEATH, STIFF, PUSH) that they entered into a computer to exit. In the movie, they escape the Maze by punching in the number sequences on the Maze's different sections.
In the book, the Mazes are located underground, beneath WICKED's headquarters. Their environments are likely identical. In the movie universe, however, the Mazes are located outside in the elements. Group A's Maze is in the desert (although the Glade is green and verdant and presumably climate-controlled), and Group B's Maze is frozen and snowy, with the walls made of ice (revealed in The Scorch Trials Official Graphic Novel Prelude). This is the one change I really kind of hate. I love the idea of the Maze being located underground; it gives an idea of false hope to the Gladers. That, maybe, at least one thing isn't being controlled by W.I.C.K.E.D., until the Ending is triggered and suddenly that reality is shattered as well. The sky turns gray, and is, to those who actually pay attention, clearly a roof high above them. The novel version also helps give readers an idea of just how big W.I.C.K.E.D. is.
In the book, the weather in the Glades is always sunny and never changes until Teresa triggers the Endingafter arriving. In the film, the weather changes, including rain.
In the book, Thomas intentionally gets stung by a Griever. In the movie, he intentionally stabs himself with the stinger that Alby chopped off from a Griever.
In the book, Thomas and Minho defeat a Griever by sending off the Cliff to survive the night, though it is later revealed that they did not in fact kill it. In the film, Thomas kills a Griever by letting it get crushed by a moving wall.
In the book, Ava Paige's name is never mentioned until the epilogue. In the movie, she introduces herself via a video once the Gladers have escaped the Maze before being rescued.
In the book, one of the rescuers tells Thomas and Teresa about the solar flares that scorched the planet and the deadly virus known as the Flare that came with it. In the movie, Ava Paige tells the Gladers about the solar flares and the Flare virus.
In the book, one of the original Gladers tried to escape the Maze by going down the Box hole resulting in being bisected. In the movie, the doors of the Box cannot be opened.
In the book, Thomas usually slept in a corner of the Glade in the forest. In the movie, he sleeps with the other Gladers in the same tent.
In the book, Thomas is attacked by Ben after following a Beetle Blade into the forest. In the movie, Thomas is attacked by Ben after Newt sends him into the forest to collect fertilizer.
In the book, Alby is described as being mean and rude. Thomas has a hard time getting along with him and getting him to explain much of what is happening. In the movie, Alby is extremely kind and Thomas has everything explained to him.
In the movie, the Slammer is called the Pit and there is no Cliff.
In the book, Ben is banished by all of the Keepers pushing him into the maze on one long pole with a collar around his neck. In the movie, they each have several smaller poles.
In the book, Minho was not with Thomas while Alby was being hoisted into the vines at the beginning of their night in the maze. In the movie, Minho was there and helps Thomas lift Alby up on the wall.
In the book, Ben was already going through the Changing when Thomas arrived, before he slips away and attacks Thomas in the woods. In the movie, Ben is seen as a healthy runner in the maze until getting stung presumably right before he finds and attacks Thomas.
In the movie, one of the major Glader rules is that no one is ever allowed to harm another Glader. However in the book, Alby and others frequently talk of pushing Gladers off the Cliff or threaten to do so to Thomas.
In the movie, there is no window in which Thomas is shown the Grievers. The first time he ever sees one is on his night in the maze with Minho. I don't like this change. I really wanted to see Thomas' reaction to Newt's "surprise".
In the book, there are 4 separate entryways into the maze, one on each wall, and at the end of the day the doors close by the right side sliding into the left. It is described as a sliding glass door, only of stone, not glass. In the movie, there seems to be only 1 entrance to the maze and it closes by both sides of the walls sliding into each other.
In the book, the entire floor of the Glade is made up of stone. In the movie, it is grass.
In the book, when Thomas sees Minho for the first time coming out of the maze early, and calls Alby, he tells them he found a dead griever. This is what leads to Alby going into the Maze with Minho. However, no such conversation is shown in the movie. Instead, Alby goes into the Maze with Minho to try and figure out what happened to Ben.
In the book, supplies like food arrive every week at the same day and time through the means of the box. In the movie it is said the supplies come up every month along with a new Glader.
In the book, Ben is a Builder, however in the movie he is a Runner. Dashner explained this was partially to provide a more clear explanation as to how he was stung.