Greg's diary is his biggest job in the series. Without it, there would be no way to to know what happens in his life. So far there have been 10 of them. The first one is red, second is dark blue, 3rd is dark green, 4th is yellow, 5th is purple, 6th is icy blue, 7 is brown, 8 is lime green, 9 is orange, 10 is black,and 11 is red-orange. All of them say DIARY on the cover. Greg exclaims how he told Susan to get one that doesn't say diary, but his mother still got one that said diary, probably because it was cheaper. All of them have little drawings between the texts based on what Greg's talking about. Each Diary has 217 pages and some of them also have 17 activity pages and the activities are extracted from the Do-It Yourself Book.
- Each diary has its own months. So far in all Diaries, there are a total of 32 months which is the same as 2 years and 8-months.
- Its owns September, October, November, December, January, February, March, April, May, and June.
- 2nd owns September, October, November, and December.
- 3rd owns January, February, March, April, May, and June.
- 4th owns June, July, and August.
- 5th owns September, October, and November.
- The 6th,7th, 8th, and 10th book have the 2 months . 6th owns November and December and 7th owns January and Febuary and 8th owns March and April, 10th book owns September and October.
- The 9th has only 1 month, June.
- In Rodrick Rules, it was later revealed that Rodrick snatched Greg's diary and ran, but tripped over a board game. Greg quickly got the diary and went to the Leisure Tower's Women's bathroom without noticing and destroyed the first diary by flushing it in the toilet. Then when the security came and got him out, Rodrick saw the whole thing and blew his secret 4-6 months later, and the story ended up changing to infiltrating the high school cheerleading locker room.
- Greg rips out certain pages of his diary, which can be seen in movies and games sometimes. In the first and second Diary of a Wimpy Kid movies, you see pages which were never in the book, meaning Greg probably ripped them out.
- Considering Greg to be 11 in Diary of a Wimpy Kid (since he was in 6th grade), if the series is not timeless,Greg would be about 13 and almost 14 (by The Long Haul, since it ends in June) but since Jeff Kinney said its timeless it is very unlikely. If considered 12 then he would be 14 (almost 15) .
- The Long Haul is the first time since the first book that there are missing months between the current book and previous book, May is missing.
- Diary of a Wimpy Kid (September-December)
- Diary of a Wimpy Kid (January-June)
- Missing months (July and August)
- Diary of a Wimpy Kid: Rodrick Rules (September- December)
- Diary of a Wimpy Kid: The Last Straw (January-June)
- Diary of a Wimpy Kid: Dog Days (June-August)
- Diary of a Wimpy Kid: The Ugly Truth (September-November)
- Diary of a Wimpy Kid: Cabin Fever (November and December)
- Diary of a Wimpy Kid: The Third Wheel (January and February)
- Diary of a Wimpy Kid: Hard Luck (March and April)
- Missing month (May)
- Diary of a Wimpy Kid: The Long Haul (June)
- Missing month (July and August)
- Diary of a Wimpy Kid: Old School (September and October)
- Diary of a Wimpy Kid: Double Down (October and November)