Each of the four main cast members - Miranda Cosgrove, Jennette McCurdy, Jerry Trainor and Nathan Kress - all made their Nickelodeon debuts on a previous show of Dan Schneider's. Miranda was a main cast member of Drake & Josh, and Jerry was a recurring cast member on that show. Jenette was in an episode of Zoey 101, and Nathan made his first appearance in an episode of Drake and Josh.
In one of the final episodes of Drake & Josh (2004), a movie title listed on the reader board of the Premiere was "Now She's Carly." This was a reference to Miranda Cosgrove (Megan on Drake and Josh) moving on to play Carly on iCarly.
Freddie often speaks some of his lines in Spanish. Series creator Dan Schneider has often stated on his blog that the reason behind Freddie's random Spanish outbursts will be revealed in a future episode, but it never was. In the final episode, Freddie began to explain it but was interrupted.
Spencer's friend "Socko" has been mentioned numerous times throughout the shows run, and it became a gag in the writing room to mention Socko's friends and family members along with their professions. Socko makes Socks, his brother Tyler sells ties. Rob is a thief. Taylor is a tailor. Otto is a car salesman. Hattie is a hat maker, cousin Isaac is an optometrist (eyes), etc.
The original title of the show was "Starstruck", and the plot followed Carly, a regular girl, who is casted on her favorite TV show. The idea was then switched to she gets her own show, and it was then changed again to she gets her own Web-show.
Most of the furniture in Carlys apartment was made by "Jellio", a company who makes furniture in the shape of cupcakes, ice cream, Rubiks Cubes and other random objects. To name a few, the hanging monkeys on the large window, the lamps, and the various colored gummy bear lamps were all designed for the show. Recently the Gummy Bear lamps have become available at the Jellio website.
Recently, Carly, Sam, Freddie, and Spencer wear several custom made t-shirts that reference several jokes from the show such as Sam wearing one that says "Church Pants", a joke from when Freddie says "She flipped out when I spilled one drop of mustard on my church pants!" in a past episode.
Sam's sound effect remote used on the show is the only one in existence. They have used the same remote since the Pilot. Dan Schneider keeps it in his home when its not being used for filming to make sure it doesn't get lost.
Lots of times, the show will reference Drake & Josh (2004), another show that Dan Schneider made. This includes Carly mentioning a Peruvian Puff Pepper, although a pepper of the same name was mentioned in Drake and Josh. Another reference is Grandad mentioning the Parker/Nichols hotel. Parker and Nichols are the last names of Drake and Josh in the series.
In a few episodes, Carly makes "special lemonade" that nobody likes to drink. This was written into the show because on Drake & Josh (2004), another Dan Schneider show, Josh Peck's character would make Limeaide that nobody liked to drink.
iCarly is the "first scripted series that will incorporate kid-created original content," according to Nickelodeon's marketing campaign and press kit. However, the content usually feature actors instead of real people.
Most of the comedic lines are improvised on set by the writers, or Dan Schneider. Most of the time the script has very few comedic lines and the comedy in the final cut of the show was improvised. The actors aren't allowed to improvise anything unless they ask the director or Mr. Schneider.
In the opening credits sequence before the music starts, some of the links in the favorites section on the screen include "TheSlap", the blog from Dan Schneider's show "Victorious", and "Danwarp", the name of Dan Schneider's actual blog.