The idea that one should dress in a professional manner (and like those who are already successful in your field) from the beginning so as to be taken seriously. John T. Malloy's 1975 book of this title (and the 1979 Women's Dress for Success) started the idea off, but others continued with it. As Molloy put it in the first book,

"FACT: Most American men dress for failure. They do so because they make one or more of four suicidal mistakes: They let their wives or girlfriends choose their clothing. They let their favorite sales clerks choose their clothing. They let designers and "fashion consultants" choose their clothing. Or they let their backgrounds choose their clothing."
Molloy himself says that he came from a blue-collar background and originally felt that as long as his clothes were decent, his ability was what was important. But when he was in his 20s, the vice-president of his department said that he needed some advice on clothes and sent him to a favorite Brooks Brothers salesman. "Each time I picked up a new suit, I reported back to my boss and he told me which of my old suits I was never to wear again. Although I did not realize it at the time, advising me on professional dress was a bigger favor than giving me a promotion." (The New Women's Dress for Success points out that men are more likely to get this kind of advice than women are.)

Molloy did a lot of research starting as early as 1963, interviewing supervisors at many companies, showing people pictures of workers dressed differently, as well as in-person experiments with different clothing, and found that small variations in clothing could make a great deal of difference. "We are more likely to open a door for a man in a beige raincoat than a black one, to hire a man wearing a blue suit than a brown one, and to believe a witness in court wearing a long tie instead of a bow tie."

Molloy's books emphasize the subtleties, not only the basic style but materials, colors, and accessories. He advises people to compare clothing sold at expensive stores and the similar items sold at lower-priced ones until they can identify the small differences that make items look higher-class and appropriate for the successful, such as "the shades of colors, the look and feel of the fabric, the way the garment is finished, the way it hangs, and its style."

His first book for women focused specifically on being taken seriously in a working world still dominated by men. "John Malloy, in his 1979 Woman's Dress for Success Book, urged women to wear a dark, skirted suit with a light blouse. He offered convincing research to back up his advice that a woman's credibility and status decreased when she wore anything else." He was also credited with the late '70s/early '80s popularity of the floppy bow tie for businesswomen as a female substitute for the male tie. However, this standard, described by one reminiscer as the "Malloy blue-suit hair-in-a-bun dress-for-success" era, was criticized for sexism (on the idea that women should not have to downplay their femaleness to be seen as equals) and later as being no longer necessary.

The expansion of "casual" businesswear, not to mention just fashion trends over the decades, have made it far more difficult for any author to set down strict rules for what is business-appropriate wear and what is not. Molloy updated the men's book in 1988, but this was before the spread of the casual Friday and casual office, so this book is probably out of date by now.

Malloy's New Women's Dress for Success (1996) is still a depressing read for anyone who believes that women have achieved equality in the workplace, because it continues to advise conservative styles of clothing (though not so limited a range as the 1970s version) and the same colors traditionally found in menswear. He still recommends skirted suits, jacket outfits, and conservative dresses, and says women should generally not wear pants to the office, and if so, they must be loose and not highlight the figure. "Our latest research shows that 6 percent of men are threatened, while 53 percent admit to being turned on by women wearing pants." He also advises against skirts above the knee for similar reasons. In general, he points out that fashion exists to make women look physically attractive and that this is almost the opposite of being taken seriously as a co-worker, even by other women. He gives some advice on particular styles for women who are unusually tall, short, or overweight, and the book contains advice on hairstyles, makeup, and accessories for all women. The New Women's Dress for Success also has a fascinating chapter on the difficulty for women in looking authoritative in "casual wear."

Unconnected to Molloy, Dress for Success is also the name of a non-profit organization which provides interview suits, professional work clothes, and other help and confidence builders to low-income women for their job searches. They have individual affiliate chapters in various U.S., Canada, England, and New Zealand cities and rely on donations of money and clothing.

Dressforsuccess.com is a men's online style guide in the same basic vein which offers a video for sale with further information about men's business clothing.

Sources:
Molloy, John T. The New Women's Dress for Success. New York: Warner Books, 1996.
http://ecglink.com/newsletter/dress.shtml
http://www.theexaminer.org/volume1/number6/wearing.htm
http://www.chanimal.com/html/dress.html
http://endeavor.med.nyu.edu/pipermail/lit-med/2004/002208.html
http://www.amazon.com/exec/obidos/tg/detail/-/0446672238/002-9947628-0136045?v=glance
http://www.dressforsuccess.org
http://www.dressforsuccess.com