A linen button down makes a great summer shirt, it protects from the sun, but it is light weight and keeps you cool. I have used linen button downs as swimsuit cover-ups and everyday wear, but they can also be worn more formally.
If your looking to buy a new one, they can be pretty expensive, but it's a good investment. Banana Republic and J. Crew have some nice ones.
Linen button downs work with a variety of trends and styles.
Pair a linen button down with khaki shorts and oxfords for a preppy look.
Wear an off-white linen button down with cargo shorts, a braided belt, wedges, a woven hat, and a leather shoulder bag for a safari-inspired look.
For a more professional look, try pairing a linen button down with a blazer, satchel, and wedges. For this ensemble I used bright colors to make it more fun.
Fashionably,
The Fashioneur