A white tie affair, such as the one President Bush hosted for Queen Elizabeth II, is the most formal event that one can host. The big difference is in attire. A black tie affair is what most Americans consider a formal affair. Men are expected to dress -- at least traditionally -- in black tuxedoes with white shirts and black ties. The traditional dress includes a dinner jacket and matching pants.
In its original form, however, black tie is considered normal for semi-formal affairs. The complimentary attire for women can range from a cocktail dress to what is considered by most to be a formal evening gown depending on the fashion and hour that the function takes place.
A white tie affair is traditionally considered an even more formal dress for men. It has very strict standards for dressing, and is characterized by a black jacket with tails, sharply cut away from the front, black pants with satin stripe, a white stiff front shirt and separate collar, a white bow tie, white vest, black socks and black shoes.