Creator Shawn Ryan's original title of the show was "The Barn." The FX network feared that potential audiences might be turned away by that, because they might think it was a gardening show or something similar. "Rampart" was also considered, after the controversial corruption charges against the Rampart division of the Los Angeles Police Department. This title was used in early promotional materials, including several TV spots. Upon opposition from the LAPD, as well as the fact that people not familiar with the Rampart scandal might not understand the name, the title was changed at the last minute to "The Shield."
Shawn Ryan has declared several times that at one point it didn't really make sense to keep the character of David Aceveda on the show, but they figured out a way to do so because they loved working with Benito Martinez.
When the show started airing, creator Shawn Ryan would notice that people were divisive regarding whether they like Vic Mackey or not and some wanted him to get caught. When Lieutenant Jon Kavanaugh was introduced into the storyline as a serious possibility for Mackey to go down, Ryan was surprised to learn that almost everyone rooted for Mackey and hated Kavanaugh.
Shawn Ryan originally wrote Claudette's character as a man. It took a call from CCH Pounder's agent to make him appreciate that a woman in the detective role would offer a whole new slant to proceedings. One thing that Ryan didn't change was the dialog, meaning that Claudette pulls no punches with her fellow detectives and the criminals she encounters. This was at Pounder's request.
To prepare for his role as Vic Mackey, not only did Michael Chiklis have to get in shape and get special training, but he learned to speak Spanish.