Black tie sets a strict rule for men (Debrett's: black wool dinner jacket, single-breasted, no vents, peaked silk lapels or a shawl collar, self-tied bow tie) but leaves women real latitude. The safe choice is the long evening gown; a very dressy cocktail dress works at most galas, outside the most ceremonial evenings. Color is free, and black is by no means required; favor refined fabrics (silk, crêpe, velvet), pumps and a clutch, with a stole over the shoulders if needed. Two traps. The first is underestimating the venue: when the invitation specifies a long gown, the cocktail dress no longer passes. The great Viennese balls, more formal still than black tie since they require the tailcoat, put it in writing: at the Vienna Opera Ball (Thursday, February 4, 2027), a floor-length ball gown is mandatory, any color admitted, with traditional costume and dirndl expressly excluded; at the Ball der Wiener Philharmoniker (Thursday, January 21, 2027), a long evening gown is required. The second is the opposite misreading: black tie is not cocktail attire, and a short daytime dress has no place there. One example on the calendar: the amfAR gala in Venice, on Sunday, September 6, 2026 at the Molino Stucky, is black tie.