Flanderization is the process through which a single element of a character's personality, often an originally mild element, is inflated in importance over the course of a work until it becomes the character's primary defining trait. The term was coined by TV Tropes, a wiki that collects and documents descriptions and examples of plot conventions and devices in fiction and pop culture, in reference to the character of Ned Flanders from The Simpsons.

Flanders himself is a complex example of Flanderization, having undergone the process in the middle seasons of the show before once again returning to a similar portrayal to his original one. Originating as "perhaps the only genuinely well-meaning, good-natured person in Springfield", Flanders was originally intended to be an ideal ("annoyingly perfect") neighbor who served as a contrast and foil for Homer Simpson. As a devoutly religious and church-going man, his faith was intended to serve as a contrast to Homer's lack of religious sophistication. However, over the course of the show's run, Flanders was simplified into a religious fundamentalist whose Christianity was his primary defining characteristic.

While Flanderization is primarily discussed in the context of fictional characters, it has also been applied to real people and historical events.