With huge ticket prices, this is a great way to protect your investment. Now dress is almost always informal. Theatremonkeys can get away with jeans, sweatshirts and trainers at all performances except first nights and the first Saturday evening of a new show when a sober lounge suit should get an airing. Comfort is first on the list. In general, suits, jackets, slacks or casual wear are acceptable for men at almost all times - casual especially during the afternoons.
Suits really are only compulsory at openings, but are frequently seen on weekend evenings.
Monkeyesses as usual have a sartorial minefield to negotiate. Dress for comfort and to embarrass any hairy companion to look good for you. As for theatremonkeys, casual is fine at most performances, dresses, slacks, jeans and sweatshirts all acceptable. Weekend evenings too can be a bit dressier than a weekday. One tip though, if sitting anywhere but the Stalls, monkeyesses should consider skirt length carefully.