In contrast to consumer fairs, only some trade fairs are open to the public, while others can only be attended by company representatives (members of the trade, e.g. professionals) and members of the press, therefore trade shows are classified as either "public" or "trade only". A few fairs are hybrids of the two; one example is the Frankfurt Book Fair, which is trade only for its first three days and open to the general public on its final two days. They are held on a continuing basis in virtually all markets and normally attract companies from around the globe. For example, in the U.S., there are currently over 10,000 trade shows held every year, and several online directories have been established to help organizers, attendees, and marketers identify appropriate events.