The majority of the episodes feature participants who have been nominated by friends, co-workers, relatives, etc., although some episodes involve self-nominations, such as the class reunion specials or mall nominations (in the latter, What Not to Wear set up its (in)famous 360-degree mirror in various malls across the United States, allowing a nominee to state her case as to why she needs fashion help).

When someone is selected, the show then secretly follows and videotapes the nominee for two weeks. Sometimes the nominee will be asked to participate in "market research," which is actually the What Not To Wear crew filming her for the show. Also, the nominators will sometimes gain access to the nominee's closet and point out specific items of clothing that they consider particularly bad.

While reviewing the secret footage, Stacy and Clinton make generally unflattering and sometimes caustic comments about the nominee's wardrobe and (in most episodes) meet with the nominators beforehand. Afterward, the entire group goes to meet the soon-to-be surprised nominee. During the surprise visit, the nominee is offered a US $5,000 Visa debit card for the purpose of buying a new wardrobe, but with a catch – she must turn over her entire existing wardrobe to Stacy and Clinton and shop by their "rules" (i.e., guidelines which are tailored toward the nominee's age, body shape, and profession). If the nominee accepts, she is brought to New York City for a week of evaluation, shopping, and hair and makeup styling. Stacy and Clinton, and in many cases the nominators, then review the secret footage with the nominee. In several episodes, the nominee admits or hints that she is either "unable" to find properly-fitting clothes or that she dislikes how her body looks.

Source: Wikipedia.org