Women who receive an invitation marked "formal dress" can assume that they should follow the guidelines of black tie. In this case, a long gown is perfectly appropriate and elegant, however, a festive cocktail-length dress or elegant dressy separates are also acceptable -- so long as they convey a sense of refinement. If the invitation specifically indicates "white-tie," however, women should wear a full-length evening gown.

The men's formal dress codes of white tie and black tie both require the elegance of a tuxedo; the former requires one with a tailed jacket, white-colored shirt and bow tie. Some formal events will denote "black-tie optional", at which either a tuxedo or a dark suit is considered appropriate. If an invitation simply states that you should arrive in "formal dress", a classic tuxedo is the most appropriate choice.

For women, a "semi-formal" dress code dictates party-appropriate attire, but it does not require an evening gown. Shorter, knee-length cocktail dresses and classic little black dresses accessorized with heels and jewelry are good choices for semi-formal events. If the event is taking place in the daytime or outdoors, such as a garden party, a nice floral sundress or dressy blouse and skirt accessorized with jewelry can also be appropriate.

While tuxedos would not be appropriate at a semi-formal event, men should remain elegant and neatly dressed and wear a dark-colored suit and tie instead. Shoes should remain dressy, and men can wear a vest or add a pocket square as accents. If a semi-formal event is outdoors or in the daytime, a light-colored suit and tie in a summer-weight fabric can be appropriate.

There are times when you might receive an invitation in which the lines between formal and semi-formal seem to be blurred. "Creative black-tie" is an oft-used dress code that still implies formal dress, but suggests that both men and women take a few creative liberties with their ties, shoes, or other accessories. By contrast "casual elegance" usually implies a semi-formal dress-code, and allows men and women to err on the side of summer or daytime suits and dresses. In these cases, however -- and whenever you're in doubt -- check with the host.