At a "formal" summer wedding—usually held in a hotel ballroom or some equally opulent setting—women are expected to wear floor-length gowns in lightweight luxurious fabrics (think: silk chiffon or silk crepe) with a tasteful neckline and an elegant silhouette. It's about looking dignified and sophisticated—not too tricked-out, revealing, or nightclub-y. To match, men should wear a tuxedo with any of the classic elements: cummerbund, peak lapel, bow tie, studs, and round-toe shoes. But a white jacket tuxedo, for example, feels lighter for formal (also called "black tie") summer weddings. If you aren't a stickler for tradition but still want to host a formal event, consider writing "black tie optional" on the invite, which allows men the alternative of a dark suit and women the choice of cocktail dresses or dressy separates.