Continuity mistake: In 2-13 "The Secret" Pam and Jim are talking about how Jim used to have a crush on Pam when she first started here. This implies that Jim was working here when Pam was hired. However, in this episode Pam says that when Jim first started working there she said, "Enjoy this moment, because you're never going to go back to this time before you met your desk-mate, Dwight." These two scenes contradict each other.
Continuity mistake: In "The Alliance" (1-4), Pam says that the next office birthday is Meredith's, but it isn't until the next month. Later, in "Survivor Man", it is said that Meredith's birthday is at the end of 'Birthday Month', when many employees have birthdays close together. It wouldn't be possible for Meredith's birthday to both be the next office birthday but also at the end of the following month, which is stated to have many other birthdays in it.
Continuity mistake: In one episode Angela says she hasn't talked to her sister in years over an argument that she doesn't remember. When she's engaged to Andy and they're touring Dwight's farm he mentions she has multiple sisters. In the finale she only has one sister and apparently they are incredibly close.
Continuity mistake: In 4-14 "Goodbye, Toby", Andy Bernard invites his parents to the going-away party for Toby Flenderson and introduces them as "Andrew and Ellen Bernard." But in 6-16 Andy tells Jim that he was originally named "Walter Jr." after his father and that it was changed when his little brother was born and the name Andrew was one that they got out of a baby-naming book. Additionally, in 8-4 "Garden Party", Dwight is introducing the entering guests. When Andy's parents arrive, Dwight says, "Mr. And Mrs. Walter and Ellen Bernard." (00:36:20)
Continuity mistake: When Jan, Michael and Pam are having a meeting in Michael's office they're sitting against the front window, but during that scene when it shows Jim and Dwight talking at their desks, if you look over Jim's shoulder you'll see that the office behind them is empty. (00:06:30)
Continuity mistake: When Michael enters the room he messes with Jim's hair and Jim's hair is noticeably different, however a few different camera angles later Jim's hair is back to normal even though he couldn't have possibly had time to touch it. (00:09:10 - 00:09:50)
Continuity mistake: When Michael takes Katy around the office, while walking by Phyllis' desk he asks Ryan to look after the purses, but Ryan says he can't because he's "installing File-Share on all the computers." Phyllis is noticeably absent from the shot. Ryan is sitting at Phyllis' desk. Michael and Katy take a few steps and walk into the kitchen area. In the background we can now see that Phyllis is now sitting at her desk and Ryan is nowhere in sight. There wasn't enough time for both to switch locations. (00:06:10)
Continuity mistake: When the Dunder Mifflin lawyer says "she thought it had to do with her recent breast enhancement surgery," the woman on the right side of the screen has her hand on her forehead. Then the shot changes angles and the woman's hand is now resting on her chin. (00:08:45)
Continuity mistake: When Jim is outside comforting Pam after she finds out her mother is dating Michael, he begins to explain a mallard recording device that Dwight gave to him and used a big hand motion that put his hand in the air. In the next shot, the hand that was in the air is now gripping his coffee cup.
Continuity mistake: When we first see what Toby's daughter looks like it's in a photograph on his desk that Michael points out in 1-6 "Hot Girl". The girl in the photo has dark brown/black hair. The next time we see his daughter is in this episode, and she has bright blond hair. A completely different child actor was used. (00:07:35)
Continuity mistake: In the first episode, where Dwight is talking to Michael and Ryan, when he gets the Jello out and gets angry at Jim, look at Jim when they keep going back and forth to him. In some shots he has a Jello cup and spoon in his hand, and sometimes he does not. (00:14:45)