The format of the show is similar to TLC's Trading Spaces (which, in turn, is based on the BBC TV series Changing Rooms).
The series began with the following premise: An individual sets up a friend or family member with a surprise room redecoration.
One of the aspects that made both Trading Spaces and While You Were Out stand apart from previous home renovation shows was that they openly depicted conflict between the cast, crew and homeowners.
The homeowner returned to find that his deck had a large hole in it, and subsequently launched into a lengthy tirade while his wife wept.
The show was first hosted by Anna Bocci, who swiftly departed and was replaced by actress and writer Teresa Strasser, who remained for the rest of the first season.
Strasser never considered herself terribly handy but compensated with her empathy for the homeowners—their travails drove her to tears on several occasions—and a sometimes dark sense of humor.
Originally during the first season, once the rooms were finished, the carpenters drove away with the show's work truck, leaving only Strasser and the designer to greet the subjects and get their reactions.
During one episode, however, the build ran so long that the carpenters were not able to leave (although the truck was hidden to avoid ruining the surprise), and they participated in the final reveal.
Since then, the format changed so that once everything was finished, the truck was driven away and the carpenters were present at the reveals, allowing them to see the reactions and accept the subjects' thanks themselves.
Due to the success of the show in Latin America, Mientras No Estabas was created for the Discovery En Español channel.