Semi-formal wear is a dress code indicating the sort of clothes worn to events with a level of formality between informal wear and formal wear. It is an outfit that is dressier than what you would wear to an office but not as dressy as a formal evening gown or tuxedo. The semi-formal guidelines lean more towards the formal if the event is held in the evening (after 6 p.m.) than if it were held during the day. Semi-formal attire is typically worn to weddings, holiday parties, and to fine restaurants. Some teen and preteen dances are designated semi-formal.

For men, the typical interpretation of semi-formal wear for evening events is black tie, and for day events, it is a black lounge suit. For women, semi-formal wear may include dresses, separates, or a suit in a dressy fabric, such as silk, cashmere, or satin. A dress or dressy suit with a dressy top, with heels, strappy sandals, flats, or dress shoes may also be worn. Sparkling gemstones, pearls, and dressy fashion jewelry are all appropriate, but it is important not to overdo it.

Semi-formal attire is a trade-off between formal and casual, and it is less formal than black-tie dress codes but slightly more formal than casual clothing. It is about striking the perfect balance between casual and dressy, and it is a notch above "business casual" but a notch below formal wear.