What to wear to a summer wedding

A summer wedding is the same event as any other wedding with two additions: heat, and ground that is not a floor. Both change what works, and neither is mentioned on the invitation.
Fabric decides your day
Linen, cotton and lightweight wool breathe. Polyester does not, and a polyester dress or a fully lined jacket in direct sun is genuinely miserable by the third hour. This matters more than colour, cut or price.
Linen creases, which is not a flaw so much as the deal. If creasing will bother you in photographs, a linen and cotton mix holds up better while staying cool.
The ground is grass
Outdoor ceremonies and marquee receptions mean lawns, gravel paths and uneven ground. A stiletto sinks. A block heel, a wedge or a flat is the difference between enjoying the day and thinking about your feet all afternoon.
Summer dress codes read slightly differently
Black tie in summer still means a dinner suit, though a lighter jacket is accepted at many. Cocktail and smart casual both relax: a linen jacket without a tie is comfortably within either at a summer wedding, where the same outfit in November might look underdone.
Plan for the evening as well
The temperature drops when the sun goes down, often sharply, and receptions run late. A jacket, a wrap or a light knit you can put on at nine is worth more than any other single item you bring.
Work out what you own first
Most people buy something for a summer wedding and then find they had a workable outfit already. Catalogue your wardrobe once, ask for something for the occasion, and check what you have before you shop.