If the wedding requires a gentleman to wear black tie (sometimes referred to as 'dinner jackets' or in America as 'tuxedos'), then it will be stated on the wedding invitation.
Traditional Black Tie
Black wool dinner jacket. Single-breasted with no vents, silk peaked lapels (or a shawl collar) and covered buttons.
Black trousers - slightly tapered - with a single row of braid down each outside leg.
White marcella evening shirt with a soft turndown collar, worn with cufflinks and studs.
Black bow tie must be hand tied; avoid novelty ties or colours.
Highly polished or patent black lace-up shoes.
Black silk socks, long enough to ensure that no leg will show between the trouser leg and sock when seated.
A white silk scarf is an optional but traditional accessory. Cummerbunds or low cut black evening waistcoats are rarely worn nowadays.