The scapular originates in the habits worn by the monastic orders, beginning with the Benedictines, and later adapted by many other religious communities. Basically, the scapular is a piece of cloth, about chest-wide from shoulder to shoulder, and drapes down the front and the back of the person with an opening for the head. At first, the scapular served more as an apron worn during work, especially farm work; consequently, in the Rule of St. Benedict identified it as the “scapulare propter opera” (“the scapular because of works”).
After the ninth century, a monk received the scapular after the profession of vows, and it became known as “the yoke of Christ” (iugum Christi) and “the shield of Christ” (scutum Christi). While certain modifications were made by the various communities, the scapular was a distinctive part of the religious habit.
Over time, pious lay people who worked closely with the monastic communities adopted a smaller version of the scapular. This smaller scapular consisted of two small pieces of cloth joined by two strings, and was worn around the neck and underneath a person’s clothing. Eventually these smaller scapulars were marks of membership in confraternities, groups of laity who joined together, attaching themselves to the apostolate of a religious community and accepting certain rules and regulations.
Eventually, these smaller versions of the scapular became even more popular among the laity. To date, the Church has approved 18 different scapulars, distinguished by color, symbolism and devotion. Most scapulars still signify a person’s affiliation with a particular confraternity, at least loosely.
Read full article for a description of the six most popular scapulars: http://catholicherald.com/stories/The-History-of-the-Scapular,4060