There is a lot of confusion over the definition of black tie dress for social invitations, so what exactly should you wear to the most formal of occasions?
Let's not be wishy-washy here: black tie is the ultimate formal occasion and you should dress with this in mind. Way back before the dress code lines got blurred, black tie for men meant a proper tuxedo coat, formal trousers, pleated front shirt with studs, a bow tie, cufflinks and patent leather shoes.
Women wore a full-length gown or an elegant cocktail-length dress with beautiful detail such as beading or sequins with open-toe high-heels and an evening bag. As fashion trends and lifestyles have become more casual, unfortunately we don't often attend black-tie events and so don't invest in formal attire.
But make the investment. As long as your waistline doesn't shrink or expand, a classic tuxedo or chic evening gown won't go out of style. After all, a well-tailored tuxedo maketh the suave man (see designer Tom Ford, pictured) and it's better to be remembered for being overdressed in an elegant ballgown than underdressed in a short sundress. Also, your host must take some responsibility.
A common gripe is when an invitation states "black tie" and the host says they wrote that because they didn't want people turning up in their work clothes or jeans. In that case, the dress code should read "cocktail attire".