Whether or not you need to wear a suit to a wedding depends on the formality of the event as dictated by the dress code, which is usually listed on the invitation. Any call for 'cocktail' or 'lounge suit' means you should wear a suit. A 'garden', 'casual' or 'beach' wedding means chinos or tailored trousers are acceptable, though you should still wear a collared shirt and blazer. Calls for 'black tie' should be met by a tuxedo and 'dinner suit' should be met with a formal dinner suit or tuxedo. If you're unsure of the dress code, a two-button wool suit in navy or grey is your safest bet, crossing over a wide range of dress codes and wedding styles.