Girl Scout cookies are any of several varieties of cookies sold by Girl Scouts of the USA (GSUSA) as a fundraiser for their local scout units. Members of the GSUSA have been selling cookies since 1917 to raise funds. Top-selling girls can earn prizes for their efforts. There are also unit incentives if the unit as a whole does well. In 2005, over 200 million boxes were sold.
I will always take the opportunity to rain on the conventional wisdome parade. There are some things you may wish to consider before supporting this form of fund raising. On first order is this news item about a current recall of cookie products: http://www.cnn.com/2010/US/02/26/girl.scout.cookies.odor/?hpt=C2 Note that the company suggests: "The company says that the odor is a result of oils improperly breaking down in the cookies … more