Picture the Normandy coast during the Great War. Coco Chanel is watching fishermen at work near Deauville in their blue and white Bretons, and she is taken enough to adapt a short, smock-like marinière for her 1917 couture collection. The French Navy had made the striped knit part of its uniform back in 1858, and Chanel took a sailor's work shirt and put it on the women of the smart set. That one borrowed shirt is still the quickest way into a riviera chic dress code.

I could not find an etiquette book that defines the phrase, so here is how I read it when it turns up on an invitation: relaxed but pressed, nautical but not costume, sun-washed colors, natural fibers, flat shoes. Nothing shiny, nothing logo-heavy. Think lunch on a terrace rather than a night out.

The stripes are the place to begin. The La Ligne Breton Tee is boxy and short-sleeved in wide black and white, with grosgrain trim, and I would wear it tucked into white trousers. The Breton Long Sleeve Tee from the same label comes in ecru with black stripes and has a boat neck, which is the right cut for a cool evening on a harbor wall. For something warmer, the Solid & Striped Hudson Sweater in cobalt and white and the Tate rugby-stripe sweater in two blues both work over a shirt collar in October.

If you want the closest thing to the original, the Saint James Minquidame is a fitted marinière in navy and ecru cotton jersey, and the Galathee II has three-quarter sleeves in ecru and maroon. Sezane's Elina Marinière is cropped, so I would pair it with high-rise linen, and the Milly midi dress is striped from top to hem. Push the sleeves up to test any of them: the stripes should stay straight across the arm.

Linen is where this dress code gets its calm. The idea that stripes and sea air belong to vacation is fairly new in France: paid vacation became mandatory there in 1936, and the Breton shirt went along for the ride. Linen did the same thing for trousers, and I would keep everything in white, sand, ecru and navy so the stripes from the first section pair with all of it.

Among the shirts, the RAILS Knox is a white button-down with mother-of-pearl buttons and button cuffs, and I would wear it open over a striped tee. Faherty's Laguna is relaxed, white and soft at the collar, which suits tucking into anything. Sezane's Julianne is the dressy one, a short-sleeve ecru shirt with scalloped, ruffled sleeve edges. On the bottom half, the Fausto trousers in mottled beige have a wide, fluid leg with lace trim at the hem, and L'AGENCE's Amara is a high-rise wide leg in pale ecru linen. La Ligne's Colby pants come in sand with fixed cuffs, and the Jenni Kayne Logan is pull-on navy with a relaxed wide leg.

My fitting-room test is the sit-down: sit, stand, and look at the lap. Linen will crease, but a good wide leg should fall straight again within a few steps. Check the hem too, because wide trousers should just clear the ground in flat sandals.

What I would skip: white head to toe, linen shirt and linen trousers in the same shade. On an invitation it reads close to wedding white, and in a photograph the pieces melt into one.

Bardot made Saint-Tropez a place people dressed for. In 1956 her film And God Created Woman put the town on the map, and the look that followed was simple dresses, bare legs, and stripes or gingham. Her 1953 Elle cover had a full-skirted gingham dress, and the lesson is that the dress does the work if the fabric is honest.

My favorites here are the pale ones. The Sea Lisette is a butter-yellow cotton poplin maxi with a square neck and ruffle trim, and the Solid & Striped Lindsay in citrina is a baby-doll tank in the same butter shade with adjustable straps and a pleated neckline. For white, the Reformation Susina is a linen midi with a sweetheart neckline and hidden back zip, the STAUD Grazia is a halter with an eyelet scalloped hem, and the Madewell Bonnie is a shift with eyelet trim and pockets. For blue, there is the Lindsay in navy eyelet, and the WAYF Mira, a navy slip midi with lace trim and puff sleeves. The VRG GRL Agnes has a pleated sailor detail at the neckline, a nod to the navy origins.

Pull the straps and the zip before you commit. Adjustable straps give you room to shift the neckline, and a hidden zip should lie flat without puckering. Pair any of these with a striped sweater over the shoulders when the sun drops.

What I would skip: any dress with a print that reads tropical. This look runs on solids, stripes and the occasional gingham, and one loud palm leaf breaks it.

Chanel and Bardot both knew the small accessories do the talking. Bardot's 1953 Elle cover had white gloves, a large-brimmed straw hat and a wicker basket, and I have never forgotten how a single hat made the whole look. Here, the hats and scarves do the same.

Start with the straw. The Janessa Leone Colette is natural raffia with a softly rounded crown and a 4.5 inch brim, made from raffia grown in Madagascar. The Waverly in bleach is wider and packable, trimmed in walnut along the edge. The Lorna Murray Tuscany Capri folds into its own bag and ties under the chin, so it is the one I would put in a weekend suitcase. Brixton's Joanna is a plain natural straw with a grosgrain band.

For scarves, I would go solid or small-scale. The DONNI. Silk Scarf in sage green is shown knotted, Sezane's Cleonie is a 105 by 105 cm square in olive with geometric stripes, and Nili Lotan's mini dot scarf is brown silk crepe, bandana style. Loeffler Randall's Beverly is silk twill in blue and cream. Tie one at the neck, on a bag handle, or over a ponytail.

Try the hat with the wind in mind: shake your head, and if the brim slides, the chin tie is worth the effort. Hold the scarf up to light too, since good silk has a soft sheen, not a plastic one.

What I would skip: a scarf with big logos, which turns an easy accent into a billboard.

The espadrille is older than any of this. The word comes from the Catalan espardenya, the canvas shoe with a coiled rope sole worn by peasants in the Spanish Pyrenees as far back as the 14th century. Castañer, founded in 1927 in Bañolas, Girona, by Luis Castañer and his cousin Tomás Serra, met Yves Saint Laurent at a trade show in 1970, and the first wedge espadrille was the result. I like that the same shoe has been on a farmer, a film star and a runway.

Grace Kelly wore espadrilles in To Catch a Thief in 1955, so I would take the Castañer Padua Mary Jane in natural canvas with a buckle strap and a braided jute footbed as the classic. Soludos does a similar Mary Jane in wheat and in pale blue. Manebi's ballet flat espadrille is a slip-on netted style with a cushioned footbed and a rubber sole, made in Spain. For leather, Sezane's Nellie is a flat fisherman sandal in glossy chocolate and the Adeline is a tan ankle-strap with a golden buckle. Ancient Greek Sandals gives you the black Eleftheria with a slim ankle strap and the gold Leda, made in Greece, with a metallic footbed.

Check the jute where it meets the canvas, because it should be stitched firmly all the way around. Wear them in before a weekend away, since rope soles loosen slowly.

What I would skip: heavy wedges for a cobblestone harbor. Flat is the whole point here.

I would build it in this order. A striped top comes first, the marinière, since it is the oldest idea in the room. Add one linen piece, trousers or a shirt, then decide whether the day wants a dress instead.

Finish with a straw hat or a silk scarf and a flat shoe, and stop. If an invitation says riviera chic and the venue is a terrace, that is enough. If it says tropical instead, the code leans toward color and print, and I wrote that one up as the tropical chic dress code. Chanel borrowed a shirt from a fisherman and made it look like freedom, and I would do the same with whatever is already in the closet.