The trench coat was designed as practical outerwear and has never really stopped being practical. It keeps off rain, layers over a sweater in cold weather, sits lightly on a jacket in mild weather, and looks right in every city in the world. If you travel in spring or autumn, it is the one coat you should own.

Job One: Rain

A good trench is made from tightly woven cotton gabardine or a technical equivalent, and sheds a shower without the look of a raincoat. With the collar up and the belt tied, it handles a wet afternoon in London or Paris better than any umbrella.

Job Two: Layering

Because it is unlined or lightly lined, a trench works over almost anything: a fine knit and trousers, a tailored jacket, a chunky sweater. Choose a size that leaves room for a sweater underneath when it gets colder.

Job Three: Polish

Thrown over jeans and a white shirt, a trench makes an outfit look considered. Over a dress at night, it looks elegant. It is the rare piece that improves whatever is underneath.

What to Look For

• Length to the knee or just below, which works on most people and covers jackets.
• A color you will wear with everything. Classic stone or khaki is the most versatile; navy and black are city alternatives.
• Room across the shoulders and back so it moves when you lift a bag into an overhead bin.
• A detachable lining, if you want one coat to cover more of the year.

How to Wear the Belt

Tie it rather than buckling it, for a softer shape. Or leave it open and knot the belt behind your back so it does not drag. On a plane, the belt keeps the coat folded neatly over your arm.

Shop the Edit

• Burberry Kensington Heritage Trench, Saks Fifth Avenue
• Max Mara Water-Repellent Gabardine Trench, Max Mara
• Alas Silk Button-Up Shirt in Milk White, Nordstrom