Children's sitcom produced originally for the Disney Channel, starring Hilary Duff. The first episode aired on January 12, 2001, and the last new episode aired on February 14, 2004, but reruns continue to air daily on the Disney Channel and on Saturday morning on ABC.
Reportedly, production of new episodes originally ended because of a Disney policy of not making more than 65 episodes of any series (a rather strange policy... why arbitrarily end a show while it's still popular?), but management started reconsidering due to popular demand and may have made more episodes, or a new series following Lizzie into high school, except that Hilary apparently wanted more money than Disney was willing to pay her. Now she's making movies for other companies, though her recording contract is still with a Disney-owned record label.
The title character was a seventh- and eighth-grader through the run of this series, attending a school variously referred to as a junior high school or a middle school -- normally, junior high runs from 7th grade to 9th grade in school districts that have such a thing, while middle school runs from 6th grade to 8th grade in districts that have that instead (though this can vary from place to place) -- Lizzie's school seems to cover only 7th and 8th grades.
She's part of a best-friend trio of two girls and a boy (Lizzie, Miranda, and Gordo), and one of the underlying themes is whether Lizzie and Gordo will ever become more than friends -- they never quite do, but lots of hints are given that they could and should. Another underlying theme is whether Lizzie's arch-enemy Kate will ever come back from the "dark side of the Force" and become a friend again -- she was formerly part of Lizzie's group of friends, but became part of the "popular crowd" and ditched Lizzie, who she now acts mean to any chance she gets. However, Lizzie still helps Kate out from time to time out of the goodness of her heart, and on rare occasions Kate has even seemed to be grateful for it, so maybe she's not completely evil after all.
The whole issue of the "popular crowd" and how Lizzie and her friends aren't part of it is a continuing source of "teen angst", but its importance is exaggerated both by Lizzie and by the self-styled popular group such as Kate; in reality, the rest of the student body has a great deal of respect for Lizzie, as shown on several occasions when they supported her when she needed it. The one time when they didn't support her -- when she lost the student election -- was when she abandoned her usual "nice-girl" personality to try to be just like the "popular crowd" -- she would have stood a better chance of winning if she had just been herself.
Themes like these raise this show above the level of just a silly kid-sitcom -- there's some genuine complexity of character behind the silly schemes and adolescent crushes that dominate the plotlines. And if much of the character motivations are rather shallow (e.g., Lizzie's continuing crush on empty-headed Ethan Craft), well, this is a show about 13- and 14-year-olds... it would be unrealistic if they didn't have some shallowness to their character.
A "gimmick" of the show is the use of the "Animated Lizzie", who appears from time to time to illustrate her unspoken thoughts.
The feature film The Lizzie McGuire Movie took place right after the end of the series, taking Lizzie on a school trip to Italy following her graduation from 8th grade, in which she ended up impersonating an Italian pop star who coincidentally looked just like her. At the end of the movie, Lizzie and Gordo really looked like they were going beyond just friends. Maybe in 20 years they'll do a reunion special in which they're married and have kids of their own.